It's normal to be nervous for a new job. Of course us with anxiety tend to amp up that nervousness to a whole new level
My advice, which is what I tell myself whenever I start a new job, is to just make it through one day at a time. That very first day you probably will just be settling in, will be shown the ropes, meet some people, etc. Doubtful they'll expect much from you - which can take some pressure off! Maybe decide to treat yourself after for getting through that first day - go to your favorite restaurant or have some ice cream or something
Then, the next day. And the next day. Take things one thing at a time. If you're super nervous, one hour at a time and take a quick break hourly (if able) even if it's just to grab a drink of water or run to the restroom.
As time goes on you will become more comfortable in the role. I always tell myself that the first month is probably going to suck, stress-wise. If after that month you're still in a state, it may be worth evaluating why. But just make it through that crummy period and you'll be fine, I'm sure
For what it's worth, I've worked a total of...four jobs (I'm still a student, so it's a large number for someone like me!) and only one have I hated so much that I dreaded going to work every day.
Best of luck and congrats on the offer!