nice attempt, I would do a number of different stacks as suggested already and then use mosaic program to stitch together rather than have DSS attempt a stitch.
here is a mosaic I did with many fov's going from carina neb to Gabriela mistral (also on goto dob)
https://www.flickr.com/photos/803366...ream/lightbox/
I ended up with a number of different images from dss then stitched in Microsoft photo gallery (probably already on your computer) - saved as tiff.
cheers