Vice principal thinks i forged my parents signature?

firstly i was suppose to hand in a form with my parent's signature on it...i'm not sure if my mum signed it but anyway i lost it... i asked for a new one yesterday and today morning i went to collect it. But after wards i found the old one in my diary already signed so i handed it in. Then at lunch the year coordinator said to me to see the vice principal. She told me and i explained everything but she didn't believe me! She said that she thought i got the form signed it then handed it in, in the morning. Anyway i explained everything... i got to admit the signature was a bit dodgey but still i am kinda sure it was done by my mum because it looks the same... anyway i told my mother after school and she said she'll back me up because she remembers looking at it but not signing it. But what if she gets called to the school? i'm scared because i have never been called to the office for anything bad and i am really really really scared plus shocked. plzzzz help me