H1B amendment shortened duration

I did change of status to H1B until July 2020. Then, they had to amend due to salary and duties change. The lawyer at our International Office messed up the application, so she requested until March 2021, but then wrote that I had permission to work until March 2020. So, of course, USCIS approved my amendment with end date March 2020. Is the best course of action to just file for an extension sometime between now and a few months before March 2020, or does exist any other way to fix this? I figured since it is not USCIS’ fault, but the lawyer/petitioner’s fault, we can’t really ask to correct an error, but we would need to file a whole new petition, correct? Will I have any issues when I go for stamping, like the consular officer being weirded out that my amendment is shorter than the initial petition?

Yes, file for extension 6 months prior to March 2020. There is nothing to be worried about, rest all should be usual with regards to stamping and other stuff.