If "where's my return" says that the return is processing then your return got accepted by the IRS. You can also use TurboTax e-file status lookup tool to check your e-file status.
You will have to file an amended return (1040X) to add the 1099G. But it is best to wait until your refund or payment is processed. The IRS will only accept amended returns via mail.
The 1040X form for 2018 isn’t ready. Please, keep checking the following information on how to amend your return; it will be updated once the 2018 form is released:
https://ttlc.intuit.com/replies/3288565
