What are the chances of getting pregnant during quick and unprotected sex that only lasts for 3 minutes? including the penis isnt very erect

No difference: Whether the sperm is delivered to the egg in 1 minute or in 1 hour, the chances of creating a pregnancy are the same. If you do not want a pregnancy, then always practice safe sex by using a condom and/or birth control pills. Erect or flaccid penises can deliver sperm to eggs equally effectively. Take no chances if your intentions are to avoid pregnancy!