Hi Bakingboju,
From what you describe, there were a number of 'limitations' based on how you were previously studying. First, it appears that you were studying just 6-8 hours a week; many Test Takers commit to studying 2-3 TIMES that (and that type of commitment is often necessary to earn a big improvement in score). Second, it's not clear how 'structured' your studies actually were - if you were working through lots of practice questions, without focusing on learning Tactics or developing specific skills (that you can use again-and-again), then your studies may have been too disorganized to be properly effective. Third, it does not appear that you were taking practice CATs/mocks at regular intervals - so you were not properly tracking your progress. That type of work (and review of that work) is necessary to define the areas that you need to work on.
Thankfully, you have plenty of time before the Round 1 application deadlines for the Schools that you listed. That having been said, you've named some highly-competitive Schools, so a strong GMAT Score will be a 'must' for your applications. As such, you're almost certainly going to have to commit to a more structured, guided and lengthy Study Plan. Based on your Score Goal, you will likely need at least another 3 months of consistent, guided study.
1) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich