Considering you're a first year medical student it's very likely that you will change your mind at least once with regard to what field you want to pursue. That being said, like it's been said before, don't aim for any specific step score, just do your best and work with what you have. I will tell you that board scores aren't everything (250/243 here with only 1 interview; although I'm carib grad), so you being in a US school already ensures you're not shutting 80% of the doors.
TLDR: do your best in class, forget about what residency you will get because you will probably change your mind a few times.