I didn't open your file (probably can't as I am still running SW2010) and I do not design products with chains or sprockets, so take my advice with a grain of salt.
You should be able to just scale up your sprocket diameter by the ratio of the number of teeth. You might need to make minor modifications, as a chain is not quite the same as a belt. It wraps around the sprocket as a polygon, not on a diameter. Going from 20 to 90 teeth, I doubt that it will make any significant difference, but see the first line of my reply.
I can't help you, but in the Bad Old days I had LISP routines that wouold do this in AutoCad. I bet someone here has a macro or a design table for this...