Why do my One Step pictures turn out half brown?

A while after I got my polaroid camera the pictures started getting this brown area at the top, like something is running down the picture. Now I can't even take pictures because they are just half brown so you can't see the image. Does anyone know what this is and how it can be fixed? I thought maybe it was water damage, but haven't really had it outside or near water, so could it be something else?

Thanks in advance for any thoughts!