Need help on pic connect 4

[lockjawz]

Im doing a pic based connect 4 using a led matrix for my senior project in high school. I am very novice at coding so please make sure to keep that in mind while critiquing my work. All i want it to do for now is to have a light at the top left to be on and when you push a button it falls down and stops at the bottom,then when you press a button again another one falls on top of that and so on. I have the first led falling but after the led stops it starts stacking until the whole left column is on. I don't know how this is possible when i have
if (b.0[rows]=0)then fall=0 : goto main
it acts if it keeps going through the loop main. Any suggestions?

fall var byte
Shift var byte
pb1 var porta.0
pb2 var porta.1
rowvar var byte
b var byte
rows var byte
stack var byte
row1 var byte
row2 var byte
row3 var byte
row4 var byte
row5 var byte
row6 var byte
row7 var byte












ansel=0
anselh=0
fall = 0
Shift = 7
down=1
portb=b
rows=0
stack=0








trisA=111111
trisb=000000
trisc=000000
trisd=000000
b=~000000
portc=000001
portd=000000










   loopa:
      portb=b+b1
       portb=b
   
    pause 500
    if (pb1==0 & b.7==0) then fall=1    
      if (fall==1) then 
        b.0[Shift] = 1
        b.0[Shift - 1] = 0
        Shift = Shift - 1
      endif
  if (b.0[rows]=0)then fall=0 : goto main
    
    goto loopa
          
 
      main:
     portb=b
       
     
      rows=rows+1
            if rows=6 then rows=0
        
       if stack=6 then stack=5
           
            
     
     if stack = 0 then b=~000010
     if stack = 1 then b=~000110
     if stack = 2 then b=~001110
     if stack = 3 then b=~011110
     if stack = 4 then b=~111110
     if stack = 5 then b=~111110
     portc=000001 
           
     stack=stack+1  
               
goto loopa