it says ending rewards on the 15 does that mean i have to take it out by then or it will be taken away
No' they will send either a gift card through email or check to you. depending on what you chose.
No. It does not add up and get banked. You get your payout every 15 days in a gift card e-mail or if you request a check they mail you the check if you make enough to get a check. You choose how you want your rewards.