Drawing rectangles in Windows Form C#

Question

Im doing a small assignment for a class where you have to create a paint application that draws circles, rectangles, lines with colors. I've done most of the work but I cant seem to get it to work properly. Right now it draws rectangles as it should (with mouse) but as soon as I want to draw another one it deletes the original and does a new one (it shouldnt do this). It does this because of the system Control.Refresh(); method Im using - but I have to use it in order to draw proper rectangles, otherwise it draws rectangles like this:

Is there a way to use the Refresh() method so it draws the rectangles correctly, but also doesnt refresh the form and delete the existing stuff drawn?

The full code I have now:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace MD4
{
    public partial class Form1 : Form
    {
        Graphics g;
        int x = -1;
        int y = -1;
        bool moving = false;
        Pen pen;
        bool line = false, rectangle = false, ellipse = false, eraser = false, penDraw = true;

        Rectangle rect;
        Point LocationXY; //Rectangle/Ellipse start location
        Point LocationX1Y1; //Rectangle/Ellipse end location

        public Form1()
        {
            InitializeComponent();
            g = panel1.CreateGraphics();
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
            pen = new Pen(Color.Black, 5);
            pen.StartCap = pen.EndCap = System.Drawing.Drawing2D.LineCap.Round;
        }

        private void pictureBox1_Click(object sender, EventArgs e)
        {
            PictureBox p = (PictureBox)sender;
            pen.Color = p.BackColor;

        }

        private void panel1_MouseDown(object sender, MouseEventArgs e)
        {
            moving = true;
            x = e.X; //Starting x and Y
            y = e.Y;
            panel1.Cursor = Cursors.Cross;

            LocationXY = e.Location;


        }

        private void panel1_MouseUp(object sender, MouseEventArgs e)
        {
            if(moving == true)
            {
                LocationX1Y1 = e.Location;
            }

            moving = false;
            x = -1;
            y = -1;
            panel1.Cursor = Cursors.Default;
        }

        private void panel1_MouseMove(object sender, MouseEventArgs e)
        {
            if(moving && x!= -1 && y != -1)
            {

                LocationX1Y1 = e.Location;

                //Refresh();

                if (eraser)
                {
                    pen.Color = Color.White;
                    pen.Width = 50;
                    g.DrawLine(pen, new Point(x, y), e.Location);
                    x = e.X;
                    y = e.Y;
                }

                if (rectangle)
                {
                    if (rect != null)
                    {
                        Refresh(); //This is the problem I think. It refreshes as soon as you start drawing a new rectangle. If I put this in the MouseMove event, the 'Pen' funciton doesnt work so it has to go here..
                        pen.Width = 5;
                        g.DrawRectangle(pen, GetRect());
                    }
                }

                if (ellipse)
                {
                    Refresh();
                    pen.Width = 5;
                    g.DrawEllipse(pen, GetRect());
                }

                if (penDraw)
                {
                    pen.Width = 5;
                    g.DrawLine(pen, new Point(x, y), e.Location);
                    x = e.X;
                    y = e.Y;
                }

                if (line)
                {
                    //NOT DONE YET
                }
            }
        }


        private Rectangle GetRect()
        {
            rect = new Rectangle();

            rect.X = Math.Min(LocationXY.X, LocationX1Y1.X);

            rect.Y = Math.Min(LocationXY.Y, LocationX1Y1.Y);

            rect.Width = Math.Abs(LocationXY.X - LocationX1Y1.X);

            rect.Height = Math.Abs(LocationXY.Y - LocationX1Y1.Y);

            return rect;
        }

        private void drawPen_Click(object sender, EventArgs e)
        {
            line = false;
            rectangle = false;
            ellipse = false;
            eraser = false;
            penDraw = true;
        }

        private void lineButton_Click(object sender, EventArgs e)
        {
            line = true;
            rectangle = false;
            ellipse = false;
            eraser = false;
            penDraw = false;
        }

        private void rectangleButton_Click(object sender, EventArgs e)
        {
            rectangle = true;
            line = false;
            ellipse = false;
            eraser = false;
            penDraw = false;
        }

        private void ellipseButton_Click(object sender, EventArgs e)
        {
            ellipse = true;
            line = false;
            rectangle = false;
            eraser = false;
            penDraw = false;
        }

        private void eraserButton_Click(object sender, EventArgs e)
        {
            eraser = true;
            rectangle = false;
            line = false;
            ellipse = false;
            penDraw = false;
        }
    }
}