Generally it's considered safe to use a condom. Good thing is, you used one, bad thing is, you are worried. So the best thing to do, don't have sexual relationship with strangers. Wait for about 03 months before you go for a blood test. It will take about 02-03 working days for the result. You can go to any neighbourhood clinic for the blood test. Till then, refrain from sex. Once you are cleared, remember to wear the helmet, get yourself a decent girl and stay faithful. You only live ONCE.