These are not flats, they look like darks or biases.
Flats are taken at dusk or dawn with a white T shirt or material over the end of the scope or with a flat light box of some sort.
They look usually white and show perhaps some vignetting depending on your setup.
How did you take these? What exposure, was it taken during dusk or with a light box etc?
Here's a sample of one of my flats that worked well:
http://www.pbase.com/image/132995797
greg.