Good question. I don't know how competitive 3.1 GPA is. In the US, it would be considered low for MBA applications. Anything below 3.5 is low-ish and more attention/focus should be give to GMAT/GRE. the advantage you have with a higher score is not only better admissions opportunities with your profile (a higher score will not get you admitted alone but it will not keep you either). However, you will be more likely to get $$ which many international applicants tend to prioritize.

In terms of chances. Add Foster here too. For now, I would say your chances would be low for Kellogg and Fuqua. You need a 325+ score for those with solid accomplishments and career goals that are feasible and doable (not a massive leap or switch). It will also help you with admissions and recruiting if you can get some experience with Tech (perhaps at your current company or startup) to show that you arenot making a huge leap and you will not be coming in to your new employer completely green. This will help both with recruiting and admissions. This could be something you can do in parallel while you are working on the GRE.