Mathematics GRE is not required for a Masters in Economics or Finance. Those programs determine admission on the basis of your grades, recommendations, any publications or research and your personal statement. In fact, the order of significance of criterion that determine admission are: recommendations, personal statement and publications, GRE general test score, GPA, and occasionally GRE subject test score. Occassionally however, a particularly brilliant performance on the subject and general test can help you gain admission to top echelon schools as they often hunt for latent talent that might be masked by lack of opportunity or encouragement.
Though having said that, however recommendations, good research/publications and you need not lose a minute's sleep over your test scores. Considering you are a graduate of the IIT university of India, I am certain you will make it to your most desirable school! Good luck!