Issues with employment

I'm 25 and I have a very spotty employment record. I have never had a job for more than 6 months and I have only been in about 3 paid positions. I find it very difficult to find and maintain work.

I got a job offer which I accepted and I am due to start on the 18th but I am just dreading it, I have worked full time before and I know I cant sustain it. From the stress it causes me at the time of working to the schedule around it, to the constant issues I have sleeping, I also have mental health issues that are likely related to being autistic and I find fitting in at any work place so hard and even if people tell me I fit in I still feel like an imposter.

But I really don't know what to do. I cant live off of my parents my entire life, I know I cant. But I just don't see how I can ever support myself and not fall apart. I just cant sustain the stress or pressure it puts on me. Its not that I am lazy or I don't want to work, I have worked hard at plenty of things that have been self driven in my life but when it comes to gaining and keeping employment it just makes me unwell. I feel like people at the jobcentre don't appreciate or understand this at all.

I have this massive conflict inside me. One side says start on the 18th and just bare it as long as I can but the other half honestly just wants to give up. I want to get a part time job but I can never find one. I am very IT literate and I have worked in IT before but because I don't have any qualifications because I was thrown off of an apprenticeship because apparently I wasn't consistent enough, and because of this no one hires me as I don't have desirable qualifications. This all came back to the fact that managing the stress of the job, as well as learning just made me ill, It was to the point where if I had some work due in 30 days I would start panicking about it even though I knew I could finish it in one day or less. I remember we had these classes that were 4 days long and took place on teams and I would sit there all day bordering on having a panic attack worrying that there would be something I couldn't learn or understand and assuming that everyone else was just better than me.

I know this has turned into a bit of a ramble, but I really don't know what to do. I just feel like I am always going to struggle to function. Like I look at my dad, he works 10-12 hours a day is fine. This job I am supposed to be starting is 8-5, so pretty standard but I am just dreading it. At my last job I managed to negotiate finishing at half 4 rather than half 5 but even that I found difficult. I just feel exhausted by it all. I don't know how people do it and sustain it but it feels impossible to me.