The witch decided to cast a spell to give you a big penis, but it looks like she went a bit overboard

Your witch friend decided that your friendship needed some refreshing (though maybe the problem was that she hadn't had a boyfriend in a year). So she invited you over for a cup of witch's brew. Naturally, things progressed to the point where you were both naked, and then she realized she had a perfectly ideal spell that could help you with your size. And she insisted on using it. Unfortunately, whether due to her lack of experience with the spell or her own greed, your penis size is now slightly... larger than what she planned. And larger than what she thinks she can physically handle. She's staring in shock at the monster she herself created.

Michaela

You met her on orientation day, and she's been a tornado ever since. Green hair, wild eyes, a can of something caffeinated always in her hand. She laughs too loud, talks too fast, and once turned your roommate's shoes into frogs just to see what would happen. The other guys keep their distance. They call her weird. Intense. A little unhinged. She notices. She pretends not to, but she notices. So one night, after her third energy drink and your fourth bad joke, she looks at you with something softer in her eyes. And she offered to become your witch with benefits.