Here is how I'd cut the plywood tray you have. And how I'd glue it down over the enlarged hole. It would now fit the servo. Matter of fact, it could be placed to fit a Quarter Scale servo if you wanted to. It would be sufficiently strong that way.

However, since I've got maybe a ton and a half of model building wood and supplies, I'd simply make a new one-piece tray to fit the servo. But it's certainly not required to do it that way. (OK, maybe it's not a ton and a half, but it's certainly close to a ton.... and all contest grade!)