1.) Show an exemplary work profile , that accounts for your weak academics. Show success at leading your business, in terms of increased revenue, and/ or improvement in your business operations. Anything you can use to quantify your contribution to your work place is good. In your essays exhibit how you have become more responsible since you left college. You dont need to be sorry, you need to demonstrate through action and achievement.
2) Do a few technical courses and score well on them. Like Accounting , Math, Statistics, etc.
3) Try to show your achievements in extra curricular work when you were in Undergrad school. Im sure keeping away from study meant you were perhaps doing something else. Were u involved in any sports, music groups, charity , social entrepreneurship or even your fathers business...
4) With regards to Knewton, its a good decision. I used Knewtons training to good effect.
Please let me know if you need a referral. Send me a pm with your email address and I will recommend you to Knewton. It will help you get a 100$ discount , on the course.
5) Dont worry to much about the past, and focus on job at hand ;which is doing well on your GMAT. Your GMAT scores are quite a critical element in the current situation.
6) Take one thing at a time. Dont rush yourself with too many things like doing your GMAT and the academic courses to make up for your grades. Unless your incredibly smart, youll mess up either or both.
7) Worry about your essays after your done with your GMAT, and improved your academic scores.