I have a hard bump under my left eyelid but you can't see it and you can only know it's there if you feel it. what do i have? i heard it can be cancer

Chalazion: At your age, by far the most likely thing is the residual leftover of your body's fight with a stye. It it cannot eliminate it, it will surround it with a cystic wall and the lid quiets down. These are termed chalazia. Cancer at your age in the lid is extraordinarily rare - so you have been mislead. If your bump is bothering you it can removed by your ohthalmologist.