Confidently incorrect, my favorite kind!
First, you counted wrong. Getting every nonsexual point possible only nets you 7 points total, not 8. Giving Magnar a wedgie doesn’t give MC a point because the DIKs see that it's clearly fake. It prevents Derek from getting the point, but that's all. Skipping out on the wedgie gives Derek his 8th point.
Second, you're forgetting about the public sex point when you fuck Quinn on the roof. That's another sexual task that can put you over the top. Derek will always get it for fucking Wendy.
Take a look.
Gay Guard Catcher
1/0
Drink 100 Beers
2/0
24/7 Dildo Helmet
3/0
Sexy Car Wash
4/1
Get Slapped 3 Times
5/1
Get Cock Signed
5/2
Prank the Alphas
6/2
Nerd Wedgie
6/2
Public Sex
6/3
Fucked a Feminist
6/4
Fucked a Teacher
6/5
Cumpetition
6/6
Tybalt's Room
7/7
Egg the Preps
7/7
If you win a point in everything EXCEPT sexual tasks (winning the Cumpetition, Nicole sucks your cock and signs it, fucking Quinn on the roof, fucking Jade and sharing the video) then you tie. And the tiebreaker is completing the impossible task: fucking a teacher.
This is straight from the code, so if you somehow managed to win while keeping your dick dry, you either cheated or misremembered.