Didn't fully pay at a buffet?

Okay so I was with my gf and we ate at a buffet, I forgot my wallet but had all but 3 bucks to pay for it, the lady took my drivers liscence and scanned it and said just bring the money back. I didn't hear here because of her accent so I walked out and wheat home with my gf. Then my gf said I think she said you were suppose to bring the money back... Anyways I forgot too, what will happen? I'm scared shitless and its oly 3 bucks?
Sorry bout the spelling I am typing on a iPad. No one needs to be jerks about this... I was asking... God damn.