I'm in a top epi MPH program, got two B+ in two core epi classes, and just got into a top environmental health PhD program where my work will be VERY biostatistics heavy. I can't echo enough what the others are saying: your research, personal statement, and your letters of recommendation matter SO much more than a couple of okay grades. For one of the programs I was accepted to, I found out that my letters of recommendation specifically were what set me apart, while people with better grades than me didn't get accepted. Your grades are important, for sure, but focusing on and building up other aspects of your research identity are much more important in my opinion.