Please help

Hey guys I really need some advise.

Today i had sex without a condom, usually my boyfriend and I always use a condom, but today we didn’t. He said he didn’t pre-cum and he pulled out way before he finished, but I am very nervous. I just downloaded the app again and It says I have a 33% chance of pregnancy. I’m not on birth control. Please help I don’t know if I should be stressed and if I should get a plan b