I am on OPT. My H1B petition was selected in the lottery. My Dso says i cant apply for STEM OPT

I am on OPT which ends on 1st of this year september. My H1B petition was selected in the lottery, but an RFE was issued.
As a backup plan, i want to apply for STEM OPT and requested my DSO of my uni to issue STEM OPT i20. But my DSO told me “you have a cap gap i-20, if we print a STEM I-20, it will be only to september 30,2017”. Is she correct? Cant i apply for STEM OPT extension for 24 months just because i have a cap gap i20 issued?

Please refer your DSO to the following and discuss further for options

its not correct you can apply for your OPT Ext…