Two solutions (pick one):
1. Set them in the scanner then READ the scanner back into Sentinel and save the profile. That way, every time you write after that your settings will be as you want them to be.
2. (perhaps easier) Change the settings in Sentinel directly. If you go this route, the tabs you want are Display Settings for the backlight and Misc for the squelch. This is all under the profile editor (EDIT / EDIT PROFILE - or just hit CTRL-1 with Sentinel open). After that, your settings will be as you want them in the scanner post-write.
What you are apparently doing is writing the 'bad' settings when you write to your scanner.
One other I would recommend you change is the opening display. Include your phone number so if your scanner is lost, and found by an honest person, they have a way to get your scanner back to you. That;s also under the Display tab. I would recommend:
Property of:
(your name)
(whatever you want here - city, profile ID, I use one of my county IDs)
(phone number)