It's good that you're getting this checked out further. Bear in mind that there are many things that can occur in the mouth that are perfectly normal. I have had many people come to me after noticing a "swelling" on their palate that has actually been there for most of their lives and they never noticed it before.

The "swelling" was actually a torus, which is a benign bony growth that some people get. It is slow growing, so rarely noticed as it grows. It is hard, because it is bone and is covered by thin, pink skin and can be quite large. It usually occurs in the middle of the palate. Now I'm not saying that this is what you have, but just pointing out that it doesn't have to be cancer.

You might want to Google "torus palatinus" and see if anything looks like yours.