Congratulations.

With NGC 6210 think small, very small. In fact it will look just like an out of focus star. Or maybe think of it this way, for the fatness it will appear, it won't seem bright enough, like a star that large will be. If you think you are in the right spot, hold your OIII filter between your eye and the eyepiece and see if it doesn't dim like the regular stars will.

Good luck.

Bill