Give me a dollar for every person who scores below his/her practice MCAT average, and I'll show you a millionaire 🙄
Seriously, though, unless your score distribution is extremely skewed, retaking with a 37 may backfire on you--adcoms may question your maturity/common sense/personal qualities, wondering why you retook with a score that's already higher than the averages at pretty much all of the top tier schools (and equal with WashU, but that school is an outlier). It reeks of egotism because there is simply no reason that a 37 would hinder you from acceptances at any schools--you seem to be retaking simply to validate your own perceived intellectual capacity.
Rather than expending the effort in retaking the MCAT (which, in your case, is a great score), you should really focus on developing your EC's, which, according to you, are seriously lacking. This will be a significantly better use of your time and improve your application much more than a few extra points on the MCAT would. Before you enter the med school application process, you need to dispel yourself of the all-too-common pre-med belief that numbers are the most important factor in an application. In reality, after a certain threshold (which you've certainly already passed), EC's become the most important in determining how schools see you. There's a reason that med school averages everywhere are significantly below a 4.0/40...there's much more to a great applicant than numbers.
PS: I was getting 39-40's on my practice tests too, and ended up with a 36...hence, I understand what you're going through.