You should not need a W-3 form since that is the form employers use as a the transmittal form for all the forms W-2 that they have issued in a given year. You use the W2-C to create your own original return if you have not filed yet, or to create an amended return and file that by mail. You can submit an amended return and pay the difference or claim a refund on the difference if it's in your favor. You can prepare an amended return with Turbo Tax or manually, but in either case, you must file a paper amended return and mail it in.
