Struggling to Keep Up with the Curve...

Ever since I started grad school, there's this constant nagging feeling that maybe I'm not cut out for it after all. It feels like everyone around me is acing every assignment and presenting their research ideas so confidently, while I'm just barely hanging on by the skin of my teeth. Last week, during a group project meeting, I managed to present something coherent but I could tell from the looks in people's eyes that they were wondering how much I actually knew about our topic... It's hard not to feel like an imposter here sometimes, you know? Am I just being overly sensitive or is this really common for grad students too? Any advice on dealing with these feelings?