Like he said!

Before you put the servo in, make yourself two small rectangular pieces of ply larger than the "ears" of the servos.

Remove a bit of covering and epoxy these pieces in on either side of where the servo screws go, to act as a reinforcement plate for the screws.

As Basinbeater mentioned, it is normal to have a gap on either side of the servo... you can shove the servo to one side, so as to center it as much as possible too.