Guess, you did not save the configuration after issuing the config-register command. Start the reload after saving the config. Before that, you could go through the following document for more details:
Upgrade Procedure for Systems Running Catalyst OS on the Supervisor Engine and Cisco IOS on the MSFC
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...