For how much? If possible, cancel the order. The 2900 is junk at this point, really not worth buying.
Anyways it does stat that I need either Two 2x3 Pin
Thats what I wrote. It will work, but you won't be able to OC using CCC. Any other overclocking tool will work. Why would an 8ppin plug work? Because it fits in the slot. Cancel the order for the 2900 and buy something better.