What type of computer do you have - desktop or laptop ? Make and model ?
It does sound like your diagnosis is very probably correct and to check it can you connect another keyboard ? Basic USB keyboards are very cheap if you can't beg, borrow or steal one to try. External USB keyboards will work with a laptop.
If you have a desktop and it turns out the Control key is stuck I would just replace the keyboard. You can do the same for a laptop but you need to check the manual, and possibly the service manual if you can find one on-line, to see what is involved. Alternatively, search on YouTube for 'Make and model, replace keyboard' and you are almost certain to find a video which will show you what is involved. Again, laptop keyboards are generally fairly cheap, it is just the amount of work involved in changing that makes it hard but even this varies dramatically from one model to another.