The gutwrenchingness of being shy

I was invited to a school mum dinner for tonight. I felt like I wasn't really who they wanted there. One afternoon at school a mum invited another mum to this thing while standing about five feet from me. They chatted for a little while and the one who had invited the other turned to me and said "Oh, would you like to come sat 3rd..." So even though I felt like an afterthought I had been invited and I don't want to be thought of a snob or anything I figured I'd go.