I would agree on the +/- 3 thing and I will give some advice.
So I did like 12 practice tests been AAMC and princeton review. First one I got like a 17 on and then by the last 4 or so I think I was at like: 30, 31, 32, 31. At this point I was still a couple of weeks away from taking the real thing. I kept taking some more practice tests so basically my average was about 31.
Took the real deal, felt relatively similar except for the physics which seems ungodly harder, ended up getting a 28.
Two takeaways:
If you are studying 30-40 hours a week, dont study past like 3 months, I think I was at 14 weeks and it was way too much.
Make sure you can find the hardest physics stuff to study. Princeton review had some challenging questions but on the real deal it wasnt like A challenging question, it was like you have to answer a chain of 3 or 4 to answer the problem fully; think final question on your final exam of your physics class, one that has a lot of parts and thought.
Overall I would still say you will most likely get +/- 2 on each section. Section wise I did very close to my practice tests, just basically 1 point lower on each section.
***Also dont freak out if you think that it is killing you while you are taking it. They curve the test based on who takes that test that day (which is why it takes so long to get your score back). So chances are if you think a particular problem is destroying you, chances are its destroying nearly everyone there.
I got 10 on my practice tests for phys/chem on like every single test. The entire time on the real thing I thought that this section was absolutely killing me, ended up with a 9. So yea, just food for thought.