No. Unlike a Cash Account, you can't withdraw from My Wagers (they have no monetary value).
Remember, when you wager with b spot, you're placing bets on live horse races. Once a bet is confirmed, the wager amount is deducted from your Cash Account and b spot places a wager on your behalf. My Wagers represent the money you wagered on the race.
After the race results are finalized, you play games to reveal your payouts. Anything you win goes directly into your Cash Account.