Upvote:7
You asked for fourteen days and they have given you fourteen days. That seems reasonable to me. They've also given you a little flexibility in your travel dates.
Whilst some changes to your itinerary are acceptable, changing your itinerary such that you should really have applied through the Italian authorities will look like visa shopping, and the immigration authorities can take a dim view of it.
If you want to go to Rome keep it to just a couple of days this time. I suspect that Paris will keep you busy enough for two weeks that a side trip to Rome will become a distraction.