You sound so thoughtful and mature, OP. You have gotten great feedback and you come across really well. I have no doubt that you will be successful!
Congrats to you for your full ride – wow. No, WOW! As our kids graduate from college, I realize more and more how hugely important it is to be able to follow your interests and passions (with or without grad school) instead of having to limit yourself. You will be able to take unpaid internships, travel, and/or know you can take out reasonable loans for grad school.
Being a big fish in a big pond ain’t bad, either. You will probably get lots of special attention and faculty mentoring. Grad school will give you a chance to have another round at admissions. By then you will have a better idea what you want to study.
Once you get on campus, become actively involved and make friends, this sense of disappointment will feel like a distant memory.
In the meantime, I would practice some comebacks that you feel comfortable with. And…come back to let us know how it is going!