Katie, I think you touch on this in some of the points you make, but how about acting as if we do belong where we are? I've found myself in a group of impressive people where I started to have feelings of inferiority or not belonging, and I found that if I take concrete actions as if I do belong (like introducing myself to people and striking up a conversation), I find the feelings tend to follow my actions eventually. My experience is that feelings tend to be a lagging indicator of reality, so if I can recognize the reality of the situation (which is admittedly tricky sometimes) and act as if it is true (which it is), then I tend to find my feelings will eventually follow.