help regarding summer courses as a biomed student

So registration through Chang has begun. I dropped chem 2 and physics 2, so I need to take them again. For now, though, I'm focused on chem 2 because it's required for most of my second-year classes, but not physics. However, I'm not sure what to do with the classes. Since chem is a continuation course, it will run from May to august. Should I take an elective as well? I hope to get into dental school, but I know that Western doesn't look at summer grades, so I don't know what to do. I also don't understand how OSAP works. Please help