Hey, how can I play this game in fullscreen mode in game? I have two black bars and it's kinda annoying. The menus works fine though. Can someone help me for this?

The dosbox config tool that gog ships with the game should have an aspect ratio toggle. Or you should be able to edit dosbox.conf to set the aspect setting (can't remember the exact name of the variable)

Use the included DOSBox Configuration utility and set Graphic Mode to OpenGLnb and under the Advanced tab check Keep Aspect Ratio. That is the original full screen mode for the game. HD/widescreen was not around then.

Thanks to Rezorrand for the tip.

Thank you! That worked!