Gravitational waves and numerical relativity is a growing field and applications to each of these fields are on the rise. It doesn't seem extremely competitive (like HEP etc.) but, is fairly competitive. With your profile, you do stand a fine chance. But, I'd suggest keeping those safe schools in which you are very very sure to get into.
Your GRE is good. Don't let it bother you too much. But, yes, do think twice before spending money on applying to places like MIT, CalTech and the "Ivy Leagues" etc., as their GRE cut-offs and standards are usually quite high. There are other universities as well where good work in GW and numerical relativity is being done. Do look them up and choose accordingly.