I hit a car in the parking lot while trying to park in a tight space but I left the scene and then came back?

I got really nervous so I fled the scene :( I know you can be charge with leaving the scene, I just got my license like a month ago. I then went back to the scene to see if I could leave them with my information like phone number or something but when I went back the car was already gone. So I called the grocery's customer service to see if anyone reported anything and she told me no and that they would of called the police. :( what should I do? I feel really guilty.