Learning Piano for 8 years - still at prelimary level?

Sorry about all the detail I just don't know what to do anymore

I first started learning piano in grade 2 so around 8 or so with a teacher at school, in about year 4 I took and passed with an A with honors or something like that prelimary level leisure or something like that AMEB exams. A year or two later, maybe grade 6 although not quite sure I was on track to do Grade 1 in the same category ( Grades weren't my main thing, I managed if anyone knows the series to do Alfred's beginner prep course A- F and then get halfway through Level 3 of the standard beginning course one) anyways, as entered grade 7 and turned 13 I became lazy and stopped going to lessons, forgetting books etc.

I moved school and stopped taking lessons, and took up saxophone for two years ( I hate it but moving on) but still tried to play piano on the side. At the start of year 10, ie this year, I started taking lessons again and started learning the piece ' Afterlife' by a7x if you don't know what it is it is a heavy metal song with heavy quaver chords in the base, pretty easy song I think it would be the difficulty of a grade 2 piece or something.

And I picked it up fairly quickly I mean I always get pieces to a messy stage fairly quickly, within a week or two, but I can never tidy them up, It's been months since I've learnt that piece and it still sounds disconnected. Until one day they just click? Is that normal ? writing that now it sounds normal but it feels like I've learnt piano wrong and now I can't start again. I think I may be trying to learn to fast and therefore can't progress because I feel like I've been playing so long so I should be better, try too hard and then never learn pieces that are 'polishable' for my ability and don't progress at all.

What should I do? Would it be better to just go back to prelimary level and learn those pieces because when I learn them I can play them quite well and learn them in a week and perfect them in 2 ( is that too fast to be learning something that makes you better? ) or continue and try not to rush it because Its only been 2 months since I picked up again and trust my teacher a bit. He lets me pick what I learn though so :) The thing is though, I have a lot of issues with not only fingering and technquie and all that jazz :) but also the proper way to learn like practice so maybe going back to square one might be helpful, if so how long would it take me to go through the grades? And what are some ways to tidy up a piece once you've learnt it ? I think sometimes I pick too many pieces at once and its too many to practice so although I could spend 2 hours practicing a night and I often do the next night I pick enough piece to practice and then I forget the first one. I'm too scared to take it slow in case it fails because I've had so many set backs.