Did the BTG core "rescan/reindex" when you put the new wallet in? If it did, you should double check your BTC addresses on https://btgexplorer.com and see if they show a BTG balance.

If they show a balance, then it's possible that either BTG Core didn't rescan/reindex properly... Or it hasn't actually started using the new wallet file that you copied in.

If the explorer doesn't show any balance, then your BTC addresses didn't contain any BTC when the fork happened.