Here's what you should do instead.
REPEAT
VSYNC 1
UNTIL (BUTTON(2) AND 16)!=0
This way, you don't even need to call labels. You can just put your game's code below the code I just gave you and it will work.
"(BUTTON(2) AND 16)!=0" is better than just "BUTTON(2)==16", because if you press, for example, A and L at the same time, the latter code won't detect the A press.
:P