Does your supervisor think you're doing ok? I constantly felt like an idiot during college.

It was nothing like high school for me.
High school academics were easy. So much of it was simple memorization of materials so that it could be duplicated accurately on a standardized test, and many homework assignments could be fired off pretty quickly.
Freshman year at college took some adjustment. University coursework took a great deal of time, and tests typically demanded that you did truly know what you were talking about. (Homework was often those infamous ones where you "only" have 3 problems to work on, but each one may take 4 hours.) Some courses allotted a full 3hr lab period to a test. Even open-book/open-notes tests would not be doable unless you already had a good grasp of what you were doing. Engineering also doesn't usually carry a reputation for being an easy field of study.
On the job: A few
years after working at the same place, I would still encounter things that made me feel a bit stupid. Some of that can be your own standards, and where they lie relative to how you're actually performing.
But if a manager or mentor there thinks you're falling behind expectations...well, then you
will need to figure out what to do about that.
"Rising junior" - probably came off bad because it's similar to the more common term "rising star," which does imply an air of "I'm so awesome you can't possibly handle it."
Old timers get a hard time here too.
Some pay extra for that....
No, just you.