Go back button

Can someone help me what I’m doing wrong?
I have this image gallery movie with background music.

I want to have “Go back” button that go back 5 frames each time someone click it.

This is the code I have but it doesn’t work.

on (release) {
gotoAndStop(_currentframe - 20);
}

I use this code for “Go forward” and it works perfectly.

on (release) {
gotoAndStop(_currentframe + 20);
}

I tried this code and “Go back” button works but the background music start splaying on each click.

on (release) {
_root.gotoAndPlay (_root._currentframe - 1)
}

I just want to go back 20 frames without disturbing the background music.
Please help.