What can you do now?
Register for a math course: If you have fared badly in any of the quant courses in college, consider doing some additional courses from recognized bodies and perform well.
Utilize the space in essays: If you did not do well in GMAT-quant, highlight the quantitative aspects of your work, where you do well. Also, see if your recommenders would like to talk positively about your quantitative skills.
If you scored below average in GMAT-verbal, highlight your interpersonal skills. Your essays should be in a flawless English. If you have been involved in business communication/presentations/editing job at your work, ask your recommenders to give examples of your proficiency in English. You may also take TOEFL and aim for a good score.
If you want to explain any extenuating circumstances which resulted in low scores, never skip the opportunity to tell the AdCom. Take full responsibility of your performance and write in your optional essay about the reasons for failure and tell about your evolution. Make sure to bring reader's attention towards other strengths of your profile.