Hi,
First, the 60th percentile is not horrible. It is merely a starting point.
How have you performed in quant-intensive classes in college? This is one method of showing that you are likely to have strong performance in business school.
There are two additional ways you can demonstrate high quant skills
1) Take additional quant classes and perform well.
2) Take the GMAT again and have a higher quant score.
Note that the GMAT is probably one of the less speeded admissions exams since it allows about two minutes per question.
It is important to recognize that some extremely bright people tend to have low scores on standardized tests just as some extremely intelligent people tend to have relatively low grades. While one can argue whether 37 questions provides a representative sample of one's true abilities, virtually every test must rely on sampling or else each test would take years to complete.
Hjort