That is so common among students they have a name for those feelings you’re facing. They call it “imposter syndrome”. It’s real to you but not real. I’m sorry you feel like this right now but focus on the prize.
You were accepted because A. They believe you will succeed there as a student in many ways. B. Because you will add something special to their campus. C. You have the academic chops.
Bottom line. You worked really hard and did impressive things to get noticed.
They are not taking substandard students at a school of that caliber. Too many candidates. Period. They guard their grad rates and other success metrics very closely.
Also, Tom Brady was a sixth round pick. He walked into the training camp and said he was the best decision they ever made and made it a point to prove it. Hard work, determination and skill. You have all those same opportunities and qualities. Go prove it and stop worrying! You got this, I promise.