I just got BTT. The first gesture I have added is specific to finder. I wanted a way to use previous and next the same way you do in a web browser, by doing a 2 finger swipe to either the left or the right.
The shortcut on the keyboard to do this is command + [. I've mapped the 2 finger swipe to this keyboard shortcut.
Now the gesture does work but not nearly as good as it does in a browser. In safari I can just do a quick flick with 2 fingers and it always registers. In finder I have to be rather deliberate about it. If I don't move my fingers exactly horizontally it will register a small vertical scroll and not the scroll sideways.
I'm using "3-finger swipe right" to go the next song and "3-finger swipe left" to control my music (next/previous song), and it works great. I have no clue, besides to check the settings for touchpad and more specifically for swipes:
I suspect yours will have the same the same values since I haven't altered mine (they are the default ones). You can also check the other settings under touchpad.
Additionally maybe you can try to record your gesture under "Drawings / Mouse Gestures"
