Always keep the negatives!
They are your highest quality original source material.
That being said, learning this lesson early is a good thing.
If the problem is due to a light leak, the camera will most likely need service. It could be as simple as replacing the light seals - which you could probably do yourself with a little research - or it could be more serious.
But before going down that path I would recommend either obtaining those negatives (if that is possible) or exposing and developing another roll of film, to see if the problem re-occurs - but get the negatives!