I think a lot of the other comments have covered that it would be best to tell your dad before this gets back to him another way, particularly if he could get blindsided at work (you'd want him to have time to think about his reaction to this, from a professional point of view, and not react immediately in anger).

However, I wanted you to know that you shouldn't feel cheap for the way your first time went. Lots of people's first times are like that, it comes from inexperience. I felt cheap after my first time too, it was with basically a stranger and I probably ended up doing things I'd have rather eased into. However, it's not a massively big deal to me now, several years on, it's not some momentous occasion or a particularly traumatic memory still. I have a great long-term boyfriend now, and that's taught me a lot about good, meaningful sex, but all my sexual experiences before then are a part of me and my journey too, in good ways and bad ways.

You're not cheap, you're worth so much more than this guy treated you like, but sometimes people are arseholes and that's not your fault. I hope you find someone you treats you right for the next time.