No, in real life, you can decide to continue your attacks until you pick up a card/make reinforcements.

For some reason, the GUI for Conquer Club makes me (maybe others) to click the wrong button on numerous occasions.

This game really, really needs some type of "Undo" button or some message asking whether or not you really want to end assaults. Yes, I should check which buttons I'm pressing, but on numerous occasions I've ended my turn prematurely by pressing the "End Assaults" button.