I'm in the same situation as you. Wrote last weekend. I answered 53, but there are at least two in there that are wrong and I remember being unsure about a bunch of others too. I'm estimating a percentile somewhere in the 70s as well. I am upset about it because I worked very hard for 2-3 months before it, but I just wasn't good enough. I guess it means that I wouldn't fit in a program like MIT or Berkeley, because I would have to work my ass off and still be at the bottom of the pack. It's better to know it now than to be stuck in it for 5 years.
But there are still really good schools that may take applicants like us if the rest of the application is stellar! Just maybe not the super selective prestigious ones. In the end, I feel like one of the most important parts of grad school is who your supervisor is. If you have a top-notch supervisor and you come up with some exciting results, then you'll land a post-doc in an awesome school. There are tons of schools with a handful of stars in their respective fields. Those are the schools that I'm going to target. I'll also throw my application around competitive programs like UCLA, UT Austin, and Columbia just in case.
Also, lot's of programs outside the US don't require the GRE. Toronto, Bonn, ETH, and Imperial are all great schools!