I don't believe that Zane was involved in setting up the sex tape, he likely isn't even aware of it. My guess is that Ethan overheard or managed to get information as to his plans for a date with Erynn and then setup a camera with the plan to blackmail her with it and here we are.
Most girls do indeed prefer to be in a relationship before taking that step, despite what porn and the media would make you believe. As for his original confession, she was embarrassed, the MC put her on the spot with Lexi and Ethan right there. It was the wrong place and the wrong time, that's on the MC not Erynn.