I just got into *my personal* top PhD clinical program with a quant score around the 50th percentile.
From what I understand, 50th percentile is pretty terrible for prospective clinical applicants. I took the GRE twice and actually scored lower on quant AND verbal the second time (after studying for another month, mind you!). You can't imagine how awful I felt after I took the GRE the second time and failed to improve. It was seriously disheartening; I felt like giving up the whole process of applying because I was sure I would be rejected. I have extreme testing anxiety but I think my AW score (90th percentile approx.) helped.
Quant is only one piece of the puzzle. I may be speaking solely from my own experiences, but my undergraduate advisers told me that they use the GRE solely to "weed out" applicants. However, a high GPA (and high grades in stats classes) and strong letters of rec can bolster weak quant scores.
My low quant score did not stop me from getting interviews. In fact, I was never asked about my quant scores (or the GRE at all). To cover my weaknesses, I made sure to ask faculty members - and my POI especially - what kinds of topics were covered in first and second year stats courses. I think showing interest in stats may help you if your quant score is not so good.
In sum: don't give up! You're worth a lot more than your score. Make sure to own that when you interview.