What kind of writing do you want to do/major in? Creative writing? Where does your interest in/experience with marine biology factor in? That really jumps out to me–I think you’d be a shoe-in as a marine biology major at a lot of places. Not to force you to do something you don’t want to do, but is there any intersection for you between your interest in writing and your experiences/internships in marine biology?
I do think you have a good shot at BU–GPA & ACT are a good match there. Are you applying to Stanford, too? Given your experience there, I would. Also, honestly you remind me of a girl I helped w/ her college apps last year who was a writer who was really into marine sciences (and had similar internship experience), and she got into Stanford.
If your focus is creative writing, there are a lot of smaller/niche schools that might be great for you. Look at Chapman, Simmons, Davidson (which has a creative writing scholarship program), Wells…