Your title refers to centering in the baseplate, but your question refers to the template.
To get good results the bushing needs to be centered in your router baseplate. Centering by eye is not good enough. To do this there is a centering tool available from the router manufacturers and also available from after market suppliers. It is basically a 1/4 or 1/2" precision ground shaft that fits into your router collet, plus a cone shaped piece with a 1/4 or 1/2" hole in the center. To use it you place the shaft in the router collet and tighten the collet. The other end of the shaft will extend through your router baseplate and/or bushing. Then you slide the cone on the end of the shaft with the narrower end of the cone facing toward the router. For centering the router baseplate, loosen the baseplate mounting screws and then push the cone into the center hole of the baseplate. The baseplate will be forced to center with respect to the router collet. While holding the cone tight against the baseplate, tighten the baseplate mounting screws. You can now remove the cone and the shaft. To center a router bushing in the baseplate, install the router bushing and then re-install the cone and shaft. Repeating the alignment process will now center the bushing with respect to the router collet. Tighten the router bushing and then remove the cone and the shaft from the collet.
When using a router to cut dovetails with the finger type dovetail jigs it isn't super critical that the router baseplate and bushing be perfectly centered, but the orientation of the router with respect to the jig needs to be maintained to get good results if the baseplate and/or bushing are not perfectly centered. I put an arrow on the top of my router bases that I use for dovetailing so that I always point the router toward the jig the same way whenever cutting dovetails so that any centering errors are always the same with respect to the cuts. (If the bushing is off center with respect to the router bit and you change the orientation of the router during the cut you will create an error equal to this offset in your cuts). Some slop between the fingers of the template and the router bushing is normal and should not be a problem if the diameter of the bushing is correct for use with the dovetail template. Most of the better dovetail jigs are supplied with router bushings that are matched to the jig since many of the bushings sold in sets are not made to close enough tolerances to get good dovetail results.
I hope I have answered your question (whichever one you had) satisfactorily.