Typically, you now have a used car and the dealer will most likely take it back but, only give you a trade in value(if buying another car) or even less money(if you want them to buy it back). They have to resell it and make another profit and commission the sales person.
There's a lot more to it than that^^^ but, you get my meaning.
Your best bet may be to keep it and try selling it now(while your driving it). You will probably get the most money this way and depending on the region you live in, you may get close(er) to what you paid for the FIT(if you had got a decent deal on the car to start with).
Honda cars have(command) a high resale value and used car prices are currently waaaaaaaay UP! This could work in your favor. Getting more back in on a trade, or having the dealer take the FIT back into their inventory is more the exception than the rule. I mean, you'd be very fortunate if this happened but, don't count on it!