I need help

So my boyfriend and I have only been dating for 5 months and we are juniors in high school. So when we first started dating after a couple months he said I love you and I still have not been able to say it back. It’s not that I don’t at all more that I am scared and how do I even know that I actually love him. Also we are waiting on sex but he still wants to do things and since he is my first boyfriend I am scared is this bad but it keeps getting brought up and I feel like it kinda messed up our relationship. Idk what to do can anyone help me.