You may need to hold the top of your mask as the air rushing past may cause it to come loose. You can also overcome this problem by tilting your head further to the right.
Finish the simulation by taking a breath from the regulator, letting go of the purge button, and inserting the mouth piece back into your mouth. It may necessary to purge the regulator (using the methods learned in Regulator Clearing)
With the regulator back in your mouth, take a cautious breath to ensure that the regulator is clear of water and then breathe normally again.