How did you find out that you missed the deadline? When did you think the deadline was? You knew you had an assignment, did you have a date in your mind when it was due in? What went wrong? - these aren't questions I need to know the answer to, but something for yourself to think about. Only you can work out what is happening here.
I don't know anything about you, and I don't think I've read any of your previous posts. You say you are undiagnosed, but that you know your brain is screwed up. Since you are on this forum, I'm assuming you think that 'screw up' in your brain is due to PTSD? If so, something traumatic must have happened in your life? (Again, I don't
need to know the answers ;))
Whatever is going on for you, probably will only only be answered, and diagnosed, and (hopefully) managed by a professional. It sounds very much like you could benefit from seeking professional help from a psychiatrist, psychologist, therapist, or counsellor. Is there any facility at your college? Someone you could speak to about your problems?
This sounds like an issue, that isn't going to just go away and get better (since you had the same problems in high school). As such I would urge you to get some professional help. In the mean time, try to be honest with your tutors. Explain that you did not know when the deadline was. Tell them you seem to be having difficulties, and ask them for extra support in this area. Ask them if it's possible to get a verbal confirmation for future deadlines. Ask them for a new deadline for the work. Since you knew you had the assignment, you will have done some work toward it, even if it's not complete yet. See if you can come up with a reasonable compromise with them.
But honestly, until you discover the main cause of your issues, and work on it (with professional help) . . .
Who knows? Possibly never.
I'm not being mean or nasty - just realistic. I spent years thinking I could sort my PTSD out, by myself. I thought talking about my 'trauma' would only make me worse. I buried my head in the sand for too many years. Don't make my mistake. Deal with this now! :)