You don't need the horn, and I would recommend against it. If you make all the right choices, you can max skill, which is all you need.
Damn uh.
Do the cheerleader quests until you can turn into a girl and take the ring from the guy, do liz's quest and lose your virginity to her BEFORE you lose it to chris, so you get skill points from Jake..train obviously......but thats all i remember from memory, just read the walkthrough in the discord