1. If your gpa is really bad your only option is a post bacc, regardless of time or whatever. This is where you retake your premed prerequisites in hopes that adcoms will like at those instead of your undergrad pre req performance
2. If your mcat is bad, the answer is to take a solid 2-3 months and get the highest possible score.
3 if you feel like both of those are fine, the answer is shadowing/clinical volunteering while doing research. Make sure your research position can lead to publications, since a lot of paid lab tech ones cannot.
If your gpa mcat clinical experience and research are all above average, you'll probably get in somewhere. if any of the first 3 things are missing it is very challenging to get in. Research is really helpful but some primary care focused programs don't really care about it.
20 months is a long time to improve your app, hah. Also just btw I got in with 3.36 science gpa but that was with a 36 mcat and pretty solid everything else. And I still didn't get into schools my friends with more balanced gpa and mcat scores got, even if their LizzyQ scores were quite a bit lower.
Don't try to make up for one area, say low mcat, by overcompensating in another, say volunteering another 300 hours.