Firstly, read the t&c’s of all bookies you sign up to, especially in regards to bonuses.
Your $100 AFL bet isn’t going to count towards any turnover requirements at BlueBet. The min odds are $1.50. You just lost $5 on that lay bet for no real reason.
Personally, for H2H sports bets like that, I wouldn’t lay the bet on BetFair. BetFair don’t care what you bet on. I’d bet on the other side of the bet at another bookie. They do care what you bet on, so doing so will get a few mug punter bets on your account.