Sometimes you have to be aggressive in your shooting. Depending on your personality, this often means going outside of your comfort zone. For example, the last time I was leading a photo tour in Burma my group was in a boat on Inle Lake. As we were stopped to shoot this beautiful temple, a dugout canoe filled with young Buddhist monks passed us by. We weren't ready for this, and we missed the best composition. So, through my interpreter, I asked the monks to circle around and pass us again. They were happy to do it, and therefore we all got excellent pictures.
If you hesitate because you are afraid to ask, you won't get the shot. Even if you are uncomfortable, ask for what you want. The feeling of discomfortable will pass, but the great pictures will be with you always.