Do you think it's fair for parents to get really upset when their kids confess things to them?

Naturally finding out after the fact is harder thanif you'd been upfront but if it were my child and I felt they were sincerely sorry after discussing all the dire consequences of your actions then I guess no harm was really done and I'd just accept that after the discussion it was over. However Im not your mum and maybe your Dad and his gf will see things differently all I can say is be open, honest and very sorry with some reurance that it will never happen again.