Jon's experience extended to one girl, so he probably wasn't any more confident than Sophie was. But with her body against his, and her lips pressed against his lips, and her skin under his fingers, confidence was suddenly less important.
Sophie's legs were all but wrapped around him, pulling him close, sending no signal at all that he should stop, but he still felt a twinge of guilt upon seeing the pain of her first time cross Sophie's face. And once, he might have stopped. But in this moment, his only thought was to help her pass through the pain with as much pleasure as he could give her.
Her pain was muffled by his lips, and her moans became louder. Her fingers gripped his hair, then the blankets, and then the sand, and then, finally, relaxed. Eventually they would part and make enjoy the island and make their way home, but for now, breathing hard and feeling their muscles relax, there was little room for anything but contentment.