If you want to keep track of your wagering when using a bonus you can do this in the 'Cashier', then going to the 'Coupons' tab, and then selecting 'Active Coupon'. Here it will show you exactly how much you have wagered so far, plus the total amount that you need to wager before the bonus has been completed.

You can also find out your remaining wagering requirements by asking a Slotastic Representative over chat, e-mail or phone.