Hmm, what is calling the function "IncreaseScore"? Is this script attached to an enemy that has a call to it on its death?
NO! You are NOT stupid.
This is an extremely common mistake. It's one you will probably make at least once on every project (multiple times for larger projects). Everyone does. It's one of many simple errors you learn to look for first so you can fix it before tweaking your code.
If you only take one thing from this experience, I want it to be learning to not get down on yourself for making simple errors and mistakes; they aren't character flaws, they're just a part of the task. NO ONE writes perfect code the first time, every coder uses a debugger.
While hardware isn't my area, my son has been learning electronics from this youtube series that says they will conclude by creating an 8-bit computer. Maybe that will help?
https://www.youtube.com/playlist?list=PLah6faXAgguOeMUIxS22ZU4w5nDvCl5gs