Three years ago, I applied RD with slightly below average SAT scores, but with an apparently bomb essay and ECs since they accepted me. If you really love BU then go ahead and do ED. I also really liked BU but opted to do RD for financial aid reasons. I still got accepted and now go here :). If you have lower test scores and can’t get them any higher then make sure you balance out that weakness with some strong essays, ECs, and GPA.