Relax, it's okay. :-) I went through the same thing. I realized that it is neither possible nor important to know a lot of stuff. It is more important and a much more satisfying experience to follow one's own interests and learn what one needs to in the process, as this kind of knowledge stays with you and does not clutter your mind. Knowing stuff is not at all as important as being able to apply logic and ask the right questions in any context.

If possible, try to work on something of interest that will take time, focus and patience to achieve, like a painting or writing poetry or coding something way beyond your current skill level. That would help your mind to calm down and focus. Hope this helps.