Yes you do

Yeah. No way are you going to cover all of your backside without some insane flexibility, which you don't have. You hope your erection would disappear or at least subside once Christina comes over. "Uh, Chris? Can you help put some sunscreen on my back?" Your voice manages to reach her ears and she perks up.

Her faint red cheeks become more apparent once she sees your shirtless self. Sure you didn't have a chiseled body or muscles that can give Arnold Schwarzenegger a run for his money, but did that really matter? "Sam. We're not at a beach, y'know?" She chuckles a little as she approaches him. "You don't need to worry about sunscreen."

"Better safe than sorry." You respond with a small amused smile of your own. Your eyes do your best to stay focused on her eyes and not somewhere less... appropriate. Now you can tell there's some crimson on her cheeks. She's getting a closer look at your chest.

You hand over the sunscreen bottle to her. At this point you only need the backside and then you're ready to go. One squirt later, she begins to apply the sunscreen onto your back. Right away, you feel how soft and smooth her hands are. Your cock agrees in its own way. You've held hands and brushed against her skin before, but nothing like this.

Christina is getting some satisfaction and enjoyment out of this. She's trying to subside her blush, but to no avail. In fact, she's feeling a little aroused. Her nipples are beginning to harden and her vagina begins to feel extra moist. Of course, you paid no attention to any of that and remained blissful of her gentle application. It feels really good.