What year model GO 170 do you have? The year model is the first couple of numbers after the "SB 170 in the serial number under the nose or by the vent plug.
If you have the older "GO" technology, then yes, use epoxy resin.
If your GO 170 has an ASA skin, I think the epoxy resin will still work, but you will need to sand/feather around your ding a bit further as the epoxy may not stick to the ASA very well.
Here's a link to board repairs that you may find useful:
Hope this helps,