Not a virgin at 15

I’m Christian and I lost my virginity at 15😬😬😬😬😬😬😬😬😬😬... yikes but like Is it a sin every time you have sex without marriage or like it’s a sin when you lost your virginity not being married? like it’s the sin every time you do it or it’s just one when you lost it? Oh and if you go for multiple of rounds it’s more than one sin?