Write a program that prints the largestof three numbers

Question

I need help with this one, but I don't know where did I do wrong?
This is my code:

.data 
numMsg      BYTE    "Enter three number: ", 0 
LargeMsg    BYTE    "Larger = ", 0 
num1        BYTE    ? 
num2        BYTE    ?
num3        BYTE    ?

.code
main proc
    mov EDX, OFFSET numMsg
    call    WriteString

    call    ReadDec
    mov num1, AL

    call    ReadDec
    mov num2, AL

    call    ReadDec
    mov num3, AL

    mov AL, num1
    cmp AL, num1

    mov AL, num2
    cmp AL, num2

    cmp num1, num2    ;Error: invalid instruction operand
    cmp num1, num3    ;Error: invalid instruction operand
    jna Label1
    
    lea EDX, numMsg
    call    WriteString
    mov num1, AL
    jmp Label3

Label1:
    
    cmp num2, num3    ;Error: invalid instruction operand
    jna Label2

    lea EDX, numMsg
    call    WriteString
    mov num2, AL
    jmp Label3

Label2:

    cmp num3, num2    ;Error: invalid instruction operand
    jna Label3

    lea EDX, numMsg
    call    WriteString
    mov num3, AL
    jmp Label3

Label3:

    exit
main endp
end main

I tried to look it up that what I did wrong, but can't, can someone help me please?