Hi there,
As this game was released in 2009, it might be tricky to get it to run in fullscreen on newer devices. If alt+enter is not getting the game to a full screen, there are a few more things you can try:
Change the Display Scale: To do this, press Win + I then click System > Display. Click the drop-down menu under "Scale/Scale and Layout" and select "100%."
Disable Full-Screen optimization: Right-click on your game's icon and select Properties > Compatibility > Disable fullscreen optimizations > Apply > OK.
Run the game in Compatibility Mode: Right-click the game's shortcut on your desktop and select Properties > Compatibility > Run this program in compatibility mode for and select an older version of Windows.
I hope this helps,