Maybe turn the car off for a couple of hours. The update may need time to complete.
If that doesn't help, try formatting and recreating the update disk (memory stick). It may have had bad data. Once you have a good one, try again. Try first without the usb stick... start the car, go to the update menu, and see if you can cancel it or restart it to gain control. If that doesn't work, try WITH the card... turn car totally off, then insert the usb stick, then start the car, then see if you can get the update to start over.
When doing these updates it is very important to leave it alone for a few hours or overnight. Interrupting it can cause trouble like this.
When I did my first update, the method that worked best was to use the "start update after I shut off the engine". Set it for 0 hours delay. Hit the START button. Wait until it shows 0% so you know it is in progress. Then get out of the car. Screen should stay on with progress display, but engine and all other lights will dim and shut off. Check back later by looking in the window. It may take anywhere from 30 minutes to a couple of hours, probably depending on speed of the usb stick. DO NOT GET IN. DO NOT START ENGINE. Wait until the screen turns off, indicating it has completed.