The key to success on your ‘first time’ is to remain calm and act like you know exactly what you’re doing. Guys do the same thing the first time they get into a woman’s pants. Now it’s your turn.
In offering his ass to you, your boyfriend is making himself extremely vulnerable and placing an incredible amount of trust in you. You must convince your boyfriend that you are up to the challenge.
At the same time, remember that the point is for both of you to have fun. If he wants you to dominate him, get into the role and claim your full sexual power. You may find yourself surprised at how turned on you get when you allow yourself to enjoy the feeling of being in control.