GMAT score often tells the admission office how well an MBA applicant can handle the courses at b-schools. So, applicants with a good GMAT will be considered strong candidates, as the admission office knows that they can learn well under pressures. Your undergraduate GPA---already spilt milk---doesn't make or break your application to b-schools. Just put it aside and focus on your GMAT and the rest of your application. A weak GMAT plus a weak undergraduate GPA would really hurt the admission office’s confidence in your candidacy.