not to shit here but i think to risk .03btc just to get .01btc for free is kinda high, even .01btc is just a bonus, someone can only send .001btc bet to oppose that .03btc so basically its a suicide for someone to bet .03btc this time. maybe if there are lots of players playing on your site it will be possible
not on really, if you bet 0.03 is both side, you can guarantee you have a stable rates. Basically you'll get payout in both case, girl or boy.
let's suppose there's 0.04 (0.03 yours) on Girl, and 0.05 (0.03 yours) on Boy.
if Girl win, you get 0.03/total girl bet = 75% value from Boy | 0.75*0.05 = 0.0375 BTC
if Boy win, you get 0.03/total boy bet = 60% value from Girl | 0.60*0.04 = 0.024 BTC
Basically you can have 0.0075 profit or 0.006 lose, this is a positive 5% EV of 0.0015/0.03
And sure, you get your bet win side back (0.03) + win that can be 0.0375 or 0.024, you'll end up with 0.0675 BTC or 0.054 BTC