Run datapump command with date timestamp and parallel parameter

I am trying to create a datapump expdp script with timpestamp and parallel parameter as below.

set currentdate=%date:~10,4%%date:~7,2%%date:~4,2%%time:~0,2%%time:~3,2%

set currentdate=%currentdate: =%

expdp ECHO/ECHO@prfecho dumpfile=ECHO_%currentdate%_%U.dmp parallel=4 LOGFILE=ECHO_%currentdate%.log DIRECTORY=DIRECTORY_ECHO

Unfortunately the dump job isnt producing 4 dump files as dumpfile is being produced as below

ECHO_201620061559_CURRENTDATE

Kindly assist.