You don't need to be absolutly original. You are making a good work, so keep it up! :)
Advices for postjam:
About castle - either add health bar or make castle more destructable (less health or visual feedback of it's destruction)
About camera. I recommend you to either cut this feature entirely (making smaller levels that fit on one screen) or redo controls - add arrows at the sides of the screen, and allow control camera position with cursor (just like any RTS do it)