Bigger bike with better brakes than you are used to.
Not too surprising you locked the rear a bit.

I was advised to 'pretend' to use the rear brake on the emergency stop. The stop in the test is always a fairly easy one to make without overshooting, so using the rear just adds the risk of what happend to you.

Good luck with the retest.
Book it ASAP or you risk a change in the rules before you take it.