A nice shot and composition. It's still a bit sharper and with better detail than the largest image is showing. I'm not being hyper critical. I have the same lens, and you shot that at 1/100th at f/5.6 and ISO 100. If you were steady enough it should have been sharper, and it is.
If you didn't resharpen (just a bit) the image during editing, that's probably your answer. Every image loses some sharpness when compressed during transfer from camera/card to computer, and it varies with tonal range and subject material.