Yep, it all looks good. The soundcard calibration file (dotted) has compensated for the soundcards inadequacies and returned a flat response for a cable (purple), as it should, since we know a cable to have a flat response.
The target line shown is for a subwoofer at a specific crossover that you have set in the left REW target panel. It is used to show how well your sub (when measured alone) tracks an ideal response. It is also used when creating filters for an equalizer.
Now you can remove the loopback cable and use that channel for your connections and measurements. Be sure to now load the SPL meter calibration file specific to your meter.