Weight Loss Challenge

I just joined a local Gym.
Was looking and the calender and seen today was weigh in day for a 6-Week Challenge.

I said what the hell so had my measurements taken. $50 buy-in $2500 winner take all.

I am a gym noob so i was wondering do i skip lifting and go for straight cardio?

Just needed a little extra motivation thats why i joined it.

Just need a little advice.

Thanks!