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If the coverage had ended, then they did not pay the Advanced Premium Tax Credit in Column C. That usually goes straight to the insurance company, so if there was no coverage, they would not have accepted a partial payment. 

It sounds as if the California Marketplace thinks the form is correct that way but the IRS will not accept the form that way.   

At the end of the day, the return will most likely be researched at the IRS if the form does not match their database.  After it is researched, they will find that there was no coverage for that month, and no premium for that month, and no need for Column B for that month. 
So if you leave all 3 columns blank for that month when there was no coverage, that should calculate the correct amount for the Form 8962 to reconcile the Premium Tax Credit. 

Obviously that is not ideal, but it should allow you to e-file, and to have the correct tax calculation, and it will most likely need to be researched in any case. 

If you would just like extra time and file an extension, it will waive failure-to-file penalties until October 18th. However, if you would have owed tax on April the 18th, the IRS will assess monthly late payment penalties and interest until you pay.

I recommend to extend your return with a TurboTax Extension and also pay your best guess of anything you may owe. If you overpay, it will be refunded. If you underpay, it will only calculate penalties on the part that was not paid.

The states vary according to their due dates and if you have to file an extension or if it is automatic. You can look it up on this TurboTax Help article and if a state extension needs to be filed, it should be an option at the bottom of the federal extension screen. 

TurboTax has a tool called TaxCaster to give you an idea of your tax liability and/or refund. You can vary different items and see how that could impact your return. Click for TaxCaster at the IRS in any event.