Pretty egret. Had it just finished shaking itself dry? I like the pose.
Shooting white bird's isn't easy. If you were off on the exposure, it sure wasn't by much. There's a lot of nice detail in the feathers, with just a few areas that are a
touch over exposed. I'm not sure what you could've done better, except for possibly spot metering off the brightest spot of the bird (not too easy to do) or maybe turn down the exposure compensation down 1/2 stop or so? The whites look fine to me, though.
Maybe it looks a bit flat because the eyes and feathers aren't that sharp? Did you try a high-pass filter or unsharp mask in post? Doing one of these should bring out some nice sharp details. Be careful not to overdo it, though - to my eye, too much sharpening makes birds look too fake.
And bumping the contrast a bit might help, too?
I really don't think you need to do much to this photo.
My 2 cents.