Congratulations, the gun looks great. Since you are new to shotguns, please consider a little free advice. Bring the gun, buttstock, up an inch to an inch and a half in your shoulder swell. Basically, you will be much more effective if you bring the sights up to your eyes, instead of your eyes to the sights. Second, pull the shotgun into your shoulder with your dominant hand and steer it with your support hand while keeping 80-85% of your weight in a foreward poisition over the balls of your feet. Again, this is only free advice based on the picture you posted. I have been a certified instructor for 17+ years and am still, always, willing to listen to and learn from others. I hope this will help. Though I carried a Remington 870 in the line-of-duty for years, my M-4 model 11721 is what I use now.
Most importantly, get as much trigger time as possible. And again, congratulations.
Scott Jens
C.H.P.D. (ret.)
Check Six Training LLC
www.chksixtraining.com