Had sex today...

It was my first time. We did it where we first met. In the lake no one was near. So we didn’t use a condom... he asked if he could continue up until he wanted to cum so I said as long as he pulled out when he felt the urge.

He pulled out seconds before he came.. could I get pregnant I’m on birth control and he said it wasn’t possible due to come ration of the lake water..