Carbonate is CO32-.
For the stoichiometry of permanganate/formate reaction it doesn't matter if the product is CO2 or CO32- - in both cases molar ratio of permanganate and formate is identical, and that's what is important for the final answer. IMHO reaction will be easier to balance with CO2 listed as a product.
No idea who will check your work and how - nitpicker may argue that you have not followed the problem verbatim.