To "screw up ___" means to make a mistake. It's a phrasal verb that can work like this:

I screwed up the recipe and it ended up way too dry.

Or like this:

I screwed it up.

You can also use "screw up" by itself like this:

He just won’t admit he screwed up.

A similar phrase is “mess (something) up,” which has the same meaning but is a little bit more polite.