When I was in college I elected to participate in programs over the summer that would earn me college credits. It wasn't as much credit as a full semester course but it still helped push me towards my goal.
What I loved about these programs is that a lot of them focused on specialized subjects. In my regular courses we often focused on survey topics and broad principles. And there wasn't much application. But in the summer we often worked on a single big project and we could focus on subjects that interested us. These courses really went a long way to developing my love of biology. I have now been a professional biologist for over 30 years.