Please contact the W2G Payer and ask for a corrected form. Meanwhile, file your return with the incorrect number. Once the IRS receives the corrected form, they will make the correction on their end and you won't have to amend at all. 

As an alternative, you can file an extension to file (but you must still pay your tax due on time, by April 18th) and wait for the corrected W2G form. Once you receive you can submit your return.