re: audio mixdown not saving multiple channnels

Good day. I recorded a b format sound sample. I imported the sample on a track set up for this format. I did some editing and then I tried to save the sample by using the command File/export/ audio mixdown where I ticked the channel batch export function and then click the precise channel I wanted to export.
When I import this new sample it comes with 8 channels instead of 4. Your help would be much appreciated. Thanks.