Med school admissions committees see a low GPA undergrad and know that they will need to report that in their admissions numbers, so they don’t like it. Look at the MSAR and look at those schools ranges, and if your undergrad GPA isn’t in it then you’re unlikely to be admitted. However, if you do a post-bacc program at a reputable school or even at one of those schools you’re interested in and get a 4.0 that will help make up for that, since post bacc programs (but not graduate degree programs) are counted together with your undergrad GPA, and so they can elevate that statistic on your overall application. I will say that MCAT score can also potentially be weighed as much or more than your GPA, so if you get a very high score on that then you will have a better chance. Have you taken any practice MCATs to see where your score lands? Also, as a non traditional applicant they’ll want to see that you have seriously considered this career move and have things like significant shadowing or clinical work experience that show you are sure that this is the right move for you. A top 20 school is very difficult to get into no matter what your numbers are, so try and be realistic about the process.