over dubbing

Hello there, i am very new to this game but enjoying the process. My question is this, having recorded a tin whistle track i followed instructions for over dubbing but listening to the original track in my headphones while trying to record the overdub it sounded very distorted. I am using a zoom H5 handy recorder as my interface, it recorded the first track perfectly and the overdub did record and play back ok but as i say the sound of the whistle in my headphones during this process was very distorted. i had the headphones plugged into the headphone socket of the zoom H5 and as far as i know followed the instructions in the manual correctly. What am i doing wrong? Thank you in advance. Mark

So the whistle is your backing track. Does it sound good in the computer? Disconnect the H5 and play the whistle into your headphones in the computer and then again into whatever your natural speakers are.

When you plug it back in, do it first, and then start Audacity.

Does the whistle have blue waves of a good size, about half-way filling the timeline space and not going all the way up and down?

Just a side point, doesn’t the Zoom have instructions to overdub without the computer? My H1 will do that.