Any major change in your life can bring anxiety, be it good or bad. You took a HUGE step getting the job and sticking out your first day! Give yourself time to adjust before judging whether you can do it or not. (At least a week.) As you get used to the new routine your anxiety will get less. Be kind to yourself, make sure you get plenty of rest at night and eat right. It's good to congratulate yourself and feel pride in what you do.