Check your motherboards manual how to make a dual-channel config.
Usually they go in slots 1 and 3 but I could be wrong about this specific motherboard.
If you problem doesnt get solved post this in the memory forums.
As long as the amount of memory in Channel 1 equals the amount in channel 2, dual-channel mode works; otherwise, it reverts to single channel. To answer your question, disregard the part about dual-channel configuration - just put the memory modules where the manual tells you to in the part about dual-channel memory configuration. I highlited those parts in red for you.