As Vid said, make sure the height of the ball guide is correct so that ball does not "pop" it out, better for it to be a bit lower if you are in doubt.

But I would disagree with the suggestion of filling the hole and redrilling it after the epoxy cures. I think doing this will almost guarantee that the drill bit will slip off of the epoxy "plug" that is in the hole and your drill bit will go wander into the much softer wood that makes up the playfield, causing the holes for your ball guide to be in the wrong/different location.

When I have had loose guides I have put a good bit of wood glue into the hole and push in the ball guide while the wood glue is still wet. Wipe up any glue that pukes up out of the holes, and some should come up, you want the holes full of glue.

Now don't touch the ball guide for at least a day. The glue will not glue the guide into the hole, but it will fill up the extra space in the hole and should keep the ball guide in place.