Please note that the only way to get the 10% boost on your own winnings or for the friend who's referred you to get the 10% bonus on your winnings is to use the referral code. If you use the link you were sent, either in an SMS, Facebook message, email, whatever, it should be prepopulated in the Referral Code box when you set up your account. This will be on the Create Account screen where you enter your birthdate.
If it's not already filled in, check the link you were sent by your friend and enter it manually, it should look like this: XXX. Unfortunately, if you don't use the referral code at sign up, you won't be eligible for the referral prizes.