When you place an order (bet) with BettorEdge, we work to match you up with others who want the opposite position. So if you take the Under, BettorEdge matches you with the Over. Because you are betting against other users and not a sportsbook, the amount people bet isn't always the same.
If you want to bet $100 on the Over, BettorEdge might be only able to find enough users taking the Under for $50 because of this, your bet will only be partially fulfilled for the $50. It might take multiple users to fulfill a bet, and BettorEdge will continue to match you with other users until your order expires.
The fulfilled part of the order will be submitted as a bet position and your unfulfilled part of the order goes right back into your account.