Double echo as in you can see the second sonar return but the unit is still showing the correct digital water depth…
or..
double echo as in the unit is showing the second return as the actual water depth on both the digital depth and the sonar chart?
If it is the second; try turning on and up the Surface Clutter menu. If you have another sonar unit running at the same time; try turning it off first to see if what you are experiencing is due to sonar interference.