Michael, I think your issue is most likely syntax related. EX3300 does NOT run ELS SW or CLI, but instead is legacy EX product (non-ELS). The correct link for configuring DHCP on EX3300 is:
https://www.juniper.net/documentation/en_US/junos/topics/task/configuration/dhcp-server-cli.html
I am guessing this is your issue. Good luck.