I have the same problem - suffered a nervous break after a bad accident at work and now only work part time. But I get so sick the night before and morning of work that I have had to call off.
I find the more days I can get myself there and get the day started the better the anxiety is. A good night sleep is essential and when my sleep is troubled I find I have even more trouble.
You have been working for this job, which means you have done this job, the only thing that has changed is the schedule, correct? So I would keep a journal or notebook with your successes, notes of thanks, positive statements that sort of thing that you can use to prove the negative nellie in your head wrong -- to say to that voice I'm not an idiot see I do do this job well, etc.
The anxiety is tough but if you find something that works for you to clear your mind - yoga, guided imagery, a hobby, meditation, breathing exercises, exercise, art, reading....we are all different. Depending on my level of anxiety I have different things that sometimes work. If I'm really anxious I don't have a prayer of quieting my thoughts with meditation, but dancing to really loud music might drown out the thoughts and get me moving in a positive direction.
We know you can do it -- hopefully others will have other ideas for you, too. I would be happy to noodle thru some with you if you would like