I contributed some money to a Roth IRA this year. Why does it increase the amount I owe? Didn't I already pay taxes on that money when I first earned it?

I paid taxes on my income last year. I then decided to put some money into a roth IRA- I know this isn't deductible. However, now I owe even more on my taxes than if I hadn't contributed any money! Aren't I now being taxed twice- first when I made the money, and now when I'm contributing it?