I hope to get into medical school after getting my B.S. in biology from UC Davis. I'm afraid to fail

You need to work on getting over this.

Even it a medical career doesn’t happen, there are MANY, MANY other professionally satisfying career paths that can enable you* “to travel the world and provide help to those who need help most”.*

When things in life don’t turn out as planned, you ALWAYS have choices. The default is not doom.