New to birth control and kinda low key paranoid?

Bailey 🌻
I'm new to the birth control life, and while I made sure to be very knowledgeable about everything before I started, I'm still paranoid about the possibility of ending up pregnant. My doctor said that it was okay for me to start my first pack the day I had my appointment on the 27th last month, since I started my period prior on the 18th in March.
 I remember her saying that it technically would be okay to go without a condom after the first week, but I remember hearing that it usually doesn't take full 100% effect until after 3 months. I just started my second pack, and my boyfriend has been really excited to try without a condom, which he's not alone I was too. 
So we made an agreement that we'd go without a condom for like a minute or two and then immediately put a condom on before continuing. I know there's the possibility of getting pregnant from pre cum but I need assurance. I'm only 19, so
I know I'm still young. Any advice or help to aid a constantly worrying mind?
edit: worth noting we just had sex which might be tmi idk i've never posted on here before so idk if that helps to know that or not