If no peer bets against your bet, then your wager becomes null and void. Your stake is refunded and essentially your bet is canceled. Should you place a wager with a stake of $100 and a bettor only lays $50 of your bet, then you only have a bet using 50% of your stake, the other $50 is not in play. Then, if a second bettor lays an extra $25, then this leads to a total stake of $75 against your bet - therefore you are using 75% of your wager and the remaining $25 in your original stake is not in play. Remember, betting in a P2P exchange requires you to essentially sell your odds.