Good grief!
How many sperm do you think it takes to get pregnant? Answer: One.
By not using proper contraception you are simply playing with a loaded gun. I'll bet you both have not seriously discussed the outcome of unintended pregnancy and what that means for you both if one decides they want the baby and the other rejects it?
You are being utterly irresponsible over your entire future and your potential child's future.
Please grow up and start taking responsibility - it may already be too late.
You are right to be worried. Go to your GP today and get a morning after prescription. Do not delay or you may easily regret your few minutes of pleasure for a very, very long time.
While you are there, make sure you discuss your options for longer term contraception, benefits and risks. Cap. IUD, oral and condoms but remember none of these provide 100% protection.