No, you cannot increase or decrease the amount of prizes on a spin wheel coupon.
Currently our spin wheels always have 8 wedges. (7 winners + 1 lose)
If you need less prizes you can create prizes with 0% in chances to obtain the same results.
Please note: On the scratch&win and Slot machine coupons you can setup exactly how many prizes you want to have. This limitation only occurs with the Spin&Win (Spin wheel) coupon.