A bit late and this may not apply to the original poster, but it should help new users of QPython to access their folders over USB.
I could not access my newly installed QPython directory (folder) from a PC through USB.
1. Depending on your phone version, when you connect the USB, you may need to use the dropdown menu on the phone to change the USB setting from charge only to transfer files.
It's really annoying but on my phone the setting defaults to charge only and you need to reset it every time you plug in the USB! (my old phone defaulted to transfer files).
2. Restart your phone after installing QPython. My QPython folders only showed up over USB after the phone restart.