HELP ME PLEASE?

So the problem that has been occuring with me since was I was very young is that, I make too much silly mistakes. For example: switching up and signs, solving , writing in place of in the next line, , etc. This has been the only reason I almost never get full grades in my school maths exam papers . How do I solve this? .

Everyone tells me that practice (especially the bashy/computational type AIME problems, I seriously have been doing a huge amount of them...) is the only way to get rid of this, but trust me, I have been seriously practising a lot lately, but still, I keep making on these types of dumb mistakes . Is there any problem in the root cause? Like something wrong with how the way I am practising? Btw my rough works are really ugly and dirty :/ is this the reason or smth? Please help me get rid of this otherwise I'll end up making sillies in IOQM and fail it this year too! .

EDIT: Failed IOQM due to just 1 silly mistake, rounded 29.29 to 30 as the silly and it was a 10 marker problem. Cutoff was 30 and I am getting 21. Only if I didn't make this silly...