The invitations you want are the ones to do work you’re afraid is bigger than you. If an invitation comes and those voices in your head answer back, “I can’t do that; I lack the expertise; I lack the experience; There are others who could do it better,” then take that as a good sign and trust the one inviting you more than those voices in your head. The inviter knows things you don’t perhaps. More importantly, the inviter doesn’t know those voices in your head (she only knows the ones in her own head).
There are simple answers to the voices, too:
You probably can do it; you have time to gather some expertise; this is the experience; and, of course, there are others who might do it better–but you’re the one being invited.
What else do you need to know?