i finished all tutorials easily and passed to galactic conquest mode

and i finished space battle then tried for winning the land battle but
i have been defeated and i quitted this mod
although i finshed space battle when i enter again
it said to me finishing space battle again but i hoped to have
land battle

that shocked me , why?

You can't save your game in the demo, and the game doesn't remember your progress. You have to play it through in one try. You quit in the middle and it forgot that you had completed the space battle.