Ideally you need another 15 hours of postbac coursework that keeps your pbGPA above 3.8x. Fifteen hours is not convincing enough, even with your engineering degree. I don't know what other biomed courses you have that are included in your undergrad GPA.
UCLA Charles Drew is more an HBCU program, so unless you grew up in a predominantly Black/redlined neighborhood, you are not likely to be a fit. That said, you did apply to Howard, Morehouse, and Meharry, three HBCU programs as well.
Maybe it's not clear how you were part of this population. How much detail did you describe your upbringing and childhood circumstances in Other Impactful Experiences or other secondary essays? Where did you grow up in California that was underserved?
Your non-clinical community service experiences do not point to the types of activities that reveal deep insights about the structural inequities historically underserved communities face. I'm sorry the start-up didn't work out, but the description does not sound like it was client-facing. Being an environmental engineer is helpful but also may not fit what adcoms are seeking.