It's hard to know for sure without knowing what made using rocket difficult for you but I have a feeling you're closet than you think!
I think (not having done them myself, only glanced at a few just now) the rustling exercises won't have gotten you used to some of the more complex types "real libraries" use. I think there are a couple of things you need to do to bridge the gap and gain confidence.
Learn how to read rust documentation (I don't mean to be rude!) The documentation usually takes some getting used to. Navigate around the rust std docs and try generating docs for a crate of your own to get a feel for it. You will need to read (some of) the rocket docs. Type signatures might look mysterious at first but once you understand the common types a library uses you'll find everything gets easier.
Read the chapter on generics in the book. You might not need to explicitly use them in your own tires and functions. But libraries like rocket will need to use them. I think reading that chapter will help even more to make the type signatures (and the errors!) involved in using a rust library easier to understand.
My final point would be to just get stuck in. You're not going to get a whole web server to compile first time using rust and that's not a problem. Read the compiler errors just as you are probably used to from rustlings and don't lose heart