IIN I've got a sti? I've only had sex with 1 guy and he was a virgin!

You are normal. Girls in porn are not normal. It took me a long time to realise that. If you boyfriend is a good person, trust me, he won't care what you look like.
And I wouldn't worry about telling your mum. I'm sure she doesn't mind. Remember that she was your age once and she has probably felt the exact way you do, worried about how she looks down there. That's what mums are for. I know it's embarrassing but she will understand. You don't need to tell her about the STI part because it doesn't even sound like one to me, you can just tell her you think you are not normal down there.
Although small white spots on the vagina area are more normal than you think. No one talks about vagina's so we don't know what's normal and that's why us women get so worried.