Green Sunfish are spawned from dirt... ok not really. But if you make a pond far from water and no fish are added Green Sunfish will eventually find there way there. That is how it works were I live in Louisiana.
Point is I would not consider starting over because they will be back either way.
The good news is that they have a large mouth so you can even catch the little ones easily. So simply start taking them out and the balance will turn towards the BG.
Around here I have noticed in ponds without LMB that the green sunfish often outnumber the BG tremendously but I have never seen that situation in a pond with LMB established.
