I'm currently in my 4th week of my first job. Honestly a small bit proud that I got a job considering my anxiety mainly as well as depression kept me from getting one.
But it has not been going too great, I cant help but to feel like I am super slow at the job and a major inconvenience to the managers. I feel like I'm using a bunch of nonexistent energy on this job so I feel like my performance just isnt that great. With that being said, i am trying what I believe is my best. Another issue is that I'm doing a very bad job at taking initiative when I need to and non-assertion has been an issue for me forever (such as speaking/asking questions/calling out for items).
I currently work 4 days a week while doing college, this has been a lot (for me of course) and recently I was planning on asking my manager if I could reduce it to 3 days. But I feel like I have no right to do that. Especially since this morning I woke up with terrible anxiety and called in sick - something I'm really embarrassed about and I hope wont become a habit (which I'm sure it wont since needless to say my anxiety did not get a lot better and only felt worse since I missed work and now I'm worrying constantly about what they think of me). I feel like it looks really bad missing work in my first month. 
I already want to quit to be honest and I just feel all around embarrassed and super weak that I cant handle it. It also concerns me and makes me feel as though I'll never amount to getting or keeping a job especially since this is a food service/kitchen job so it's technically supposed to be pretty basic.
I've just been filled with fear that they're going to fire me, and I've been filled with so much exhaustion and disappointment next to that.
Now I'm not sure if I should just quit, or ask for the reduced work days, or just suck it up and keep going till they kick me out.

Beyond my personal situation/experience , I honestly welcome any general advice to keeping a job while struggling mentally.