Double sound on playback

[Judesse]

First time user here. At first I couldn't get the audio to work at all, but then found the advice to go into my computer settings and allow stereo mixing. I did that and when I tested it for a minute it seemed to work. Then I recorded an hour long performance and when it plays back there is an echo of the sound, in other words, it's like you hear someone talking and then hear the same thing again a second later over the top of it, like an echo. I'm not sure why this happened? Any ideas? Other than that, the Debut worked great.