You'll be fine. If you're worried, there's nothing wrong with injecting 1.5cc in one and 1.5 cc in the other. Personally, the less stuff in my ass, the happier I am.
My last cycle was 3cc in each shot and you definitly need to apply pressure right after the shot. A nurse told me if you keep some air in the syringe( 2 slashes on the side of syringe) that will help form a seal. Good Luck