Do you ever just stop talking in the middle of a group conversation because you think you are bothering people?

yes

I sometimes trail off and mumble until going quiet.
It's less because I think I'm bothering them and more because I think I sound stupid.

Somehow I doubt people feel you're bothering them, you seem very polite and you're shockingly beautiful

Sometimes I feel as though I can't find a good spot to jump in because people are demanding the spotlight, so I just back down and let it happen.

It's not just you.

All the time.