If it remains in Demo mode then I guess something is wrong with the activation of the software. Uninstall it again, remove the registry entry and reinstall. Choose the Offline Activation Method. It is very easy to do:

If you are unable to use instant Online Activation you can try to activate product manually Offline. (ignore this line)
- First of all please make sure you have the latest version of the product
- GENERATE AND SEND YOUR SYSTEM CODE.
- Run a product installer .exe file at your computer upon which you intent to use the product.
- Review the license terms and click 'I Agree' if you accept them to proceed.
- Select Manual Offline Activation method.
- Submit Activation Request: enter the Order Number (make sure you enter correct Order Number for the product you are activating!) and valid e-mail address. Please double check you enter Order Number and e-mail address WITHOUT SPACES
- You will get a message that System Code file has been generated and saved to selected location. Click 'Next' to continue.
- Transfer System Code (code_xXXX.txt) file to any computer connected to the Internet.
- At the computer connected to Internet open this page. Click 'Browse' and select the System Code (code_xXXX.txt) file. Press 'Send a code'.
- System will connect to our server and generate a Key file.

HOW TO USE THE KEY FILE:
- Save generated Key (key_xXXX.txt) file. Do not rename it!
- Transfer the Key (key_xXXX.txt) file to your MSFS gaming computer.
- Run the product installer file (.exe)
- Choose 'Manual Offline Activation'
- Choose 'Use a Key received from Captain Sim' and follow the installer prompts.

From: General / Download/Installation (QID 31)

Mark