Ok, not too bad for the age of the chick. If possible I'd drop the cooler side down further (like another 5-10F) but that might not be feasible so don't sweat it if you can't.
I really don't do anything special for pasty butt other than keep checking and keep clearing. My chicks just get...
It should be fine, it's just a bit of fluff.
I find heat to be a contributing factor to pasty butt so depending on what you're using for heat (i.e. heat lamp) you might want to drop it a few degrees, or check that you have an adequate amount of cooler space for the babies to use.