I can't give you any specific advice on an instructor or class in your area.
If you are not using it now, download ViewNX2 from the nikonusa.com site. That will let you downsize and crop images for posting. It will also show you your focus point. Just don't get confused on that point if you are doing something like focus and recompose. In that case the actual focus was somewhere else
Which 300mm lens model do you have?
Eric just gave you some good advice- test the lens against something easier in order to eliminate that variable.