What to do if Post Completion OPT expires before receiving STEAM Extension EAD

[aas312]

My Post Completion OPT Expires on May 23rd 2014. I applied for extension on April 18th and USCIS office received completed application on April 21st. If I do not receive my STEM EAD before May 23rd then what are my options? I filed the application online and it was submitted to the Nebraska Service Center. 

[newH1B2014]

You can work  max six months after opt end date .