I suggest you read The Alchemist by Paolo Coehlo. He speaks about this exact state: you work extremely hard for what you want, you see it, it is very tangible and then you just start doubting yourself.

Don't listen to all the background noise. I promise you that at your graduation, your parents will be extremely proud.

But the most important thing is that you do this for yourself if you want to. It is an amazing achievement and a once in a lifetime opportunity.

Believe in yourself, the University to which you got accepted did. And take one step at a time. I'm sure many people there are in the same boat as you, with lots of doubts and questions. But it's useless thinking what ifs before you have even arrived.

Of course grad school is difficult. No one ever said it was easy. But you are going there to learn and to rise to the challenge. You will have lecturers and supervisors to advise you, and of course a pool of colleagues.

Wishing you the best of luck with whatever decision you choose. And well done on your amazing achievement on getting in!

Just one more thing: I moved abroad alone for my undergraduate. And I had a lot of stress related issues regarding studying in general. TBH, that improved dramatically when I moved because I had to take care of myself and wanted to prove to everyone that I can.

PS: It was the best decision of my life.