What other people think you're capable of is irrelevant. You're not incapable of anything. Just work hard to do what you want to do.
You can only ever not do something if you don't try. As long as you stay motivated and keep working hard, you can do whatever you want. (within realistic expectations obviously. I mean, you might be able to attain godhood if you try really hard, but it may take a while)
My mum and half my teachers thought I was going to fail everything in school. They had a good reason to think that(I was very ill), but I still proved them wrong in the end, so don't rely too much on your mum's presumptions.