3 sciences is definitely doable. You just have to be really serious about studying, in whatever way works for you. For me that was going to all classes, taking good notes, and then cramming a couple of days before the tests. For others it is a more steady, every day review thing. You just need to find your groove and get into it. I did 4 science classes one semester + volunteering and I was constantly either in lab, class, volunteering of the library. It wasn't the most fun semester ever but it worked and in the end I agree that it does show adcoms that you can do some intense science workloads. Good luck 🙂