I do get insecure about my intelligence sometimes. I reassure myself by remembering what I practice, what I'm good at, and my experience, and then I realize how badly other people would handle it compared to me.

Most of the time, intelligence isn't an absolute value. So, remember what you're good at and stick with it.

You need to start seeing intelligence as "this is what I've adapted and gotten used to" instead of "why can't I solve multiple math problems in my head simultaneously?" University isn't terribly hard, most of the effort comes from trying to manage your time well.

That's really about it. I see programming as a theme here, so all you need to do is just practice and get yourself used to it daily and read people's writings online. Start as slowly as you need to - one could learn any language if he merely sees one word a day.

Just chill out and remember, being "dumb" isn't terribly bad. Get yourself to admit it, move on, and do things better than other people. What's the point of getting flustered when there are truly dumb people who never get insecure?