Does anyone else feel like they don't "work hard" enough?

So I'm gonna be back at school soon (it's currently the summer holidays rn) and I'm not looking forward to school. I've recently entered the senior phase of highschool (year 4 to 6 is senior phase at this school) and uggghhhhh I don't mind school but the past year or so I just haven't felt like I've worked hard :( I just haven't cared about school for awhile now and omg I need to LOCK IN THIS YEAR BECAUSE I HAVE PRELIMS AND ESSAYS AND EVEN EXAMS so much to do and I just feel like I can't do it all, im a slow worker and I just can't work quicker bruh. I can't even study properly. (I have got diagnosed for adhd/add, but that can only go so far in terms of extra time and support). I have a persuasive essay to do in English and I've lost interest in what I want to write about as well, it's probably too late to change subjects (and I suck at writing and hate big having to write big pieces). I having to relearn a whole subject as well (graph comm). 

Does anyone else struggle with this? I should just shut up and try but, I can't help but worry about it

If anyone has any advice for me? It'll be a big help, byeee