need Lowrance help

I have a 480m sonar/gps. I have the navionics chip for In,Il etc when I bring up the lake I am on and the satellite signs on. I zoom in to see the area I am on when I get it to the level on the map I like and the sonar side is on I am done . start fishing within 2 minutes or less the map zooms back out to the state still showing the cursor where I am. How do I lock it at the zoomed in level I want? help please I am going tomorrow and would like to spend more time fishing than messing with the electronics