I think the Orlando FSDO at some point had less then a 10% first time pass rate on CFI applicants.
I've always understood that you get a pass on an Initial CFI fail because nationwide the first time fail rate is so high.
Take the blame for the fail though, own it.
Don't tell them you failed because you CFI didn't prepare you, the FAA dude was being difficult and your mom forgot to make you lunch.