First of all, the AD620 is an instrumentation amplifier, not a comparator. You COULD, I suppose, make it work as a comparator, but why?
If the assignment is to use the AD620, then maybe you should use it for it’s intended purpose, like amplifying the output of the LM35. The way you’re using it doesnt take advantage of the whole reason for using an INAMP to begin with (common mode rejection).
Secondly, I don’t think its a good idea to drive an LED directly from the AD920.
Thirdly, why do you think you need a filter?