It's wings should be a little bit bigger and wider in order to realistically support it's massive weight (at least as big as it's body, like the official Pokemon sketch), but other than that, it looks amazing!
The wings are actually more or less the same size as the one shown in the original anime drawing (which, under scrutiny, may not provide flight on their own. Wing beats per second, and other biological structures such as hollow bones also come into play).
I don't base my interpretations on type or egg groups, but merely on its design. I've seen much more insectoid interpretations of Flygon that suggest it is fully an invertebrate and thus fits in the bug egg group better than mine. I depict it as half bug, half reptile, so-to-speak. Realistically, it would have it's own taxonomic class and thus an egg group of its own