Hello Sarah,
Sadly, I do not have much personal experience with Polaroid cameras, but my sister did have this issue herself and it was because the film was exposed to air before being used to take a picture. I would just recommend buying another pack of film. If the issue does persist, it may be something worse, such as an internal issue, but I believe the film was just exposed to air. It takes less than a few seconds to ruin film exposed to air.
Hope this helps!