There's a lot going on in this code, and it's not clear to me which plot is the one you're having trouble with. I think it will be a lot more likely that someone will be able to help you if you can cut this down to a minimal, reproducible example? That means isolating just the ggplot2 code that is causing you trouble and providing enough sample data to demonstrate the issue.
For more on the nitty-gritty of how to do this: