Ditto ... head and neck is the kill region. Ditto ... pellet count in the kill zone advice is right on.

As far as "adjusting" pattern, I know of no way to "fill" holes in a particular pattern other than changing shot shell or choke. If it is point of impact that is off, you can either aim compensate (which would be tough for me to do), adjust the sights if possible or try an after market sight system.

In my book patterning is a must. And I would use a "turkey" target. If the pattern is evenly dispersed with 8-10 pellets in the kill zone at 35-40 yards, it is a good choice. If it is not evenly dispersed or the number of pellets in the kill zone is weak, then buy another and try it. Lots of folks go for a 3 1/2" shell. I am one that does, though I do not believe it is a neccessary evil. The recoil can be evil and you may not want to deal with that.

You may also want to try a screw in "turkey choke". Several good ones are out there. These are typically an X-Full to X-Full+, ported, barrel extender.

If you are not familiar with shot shells labeled specifically for use on turkey, you can pay from about $1 each to about $10 each. Most will be #4 to #6 shot or some mix of shot size (such as the Nitro brand). Depending upon which brand you buy.

Good luck and hope you bag a good 'un.