1)Install menuhax
2)configurat to auto boot (press no button I hope u know how u do this)
3a)I prefer this because I don't really know if the normal 3dsx (from the gateway zip works and with that you will still be able to use HBL)download gateway_cia.7z (it's here in gbatemp) and install it
3b)take the gateway 3dsx from the gateway zip and rename it to boot.3dsx and drag it in the root of your sd card
4) fin
I hope it works