Assuming this was an accident, it is likely that nothing in particular will happen. Despite this, it is best to avoid creating such situations. Common mistakes include: accidentally opening two tabs of the game and then acting within the game OR issuing an instruction before the previous one was processed (happens on slow connections and during periods of lag).
The first can easily be avoided by playing the game in its own screen (as the "Launch Game" button on the Core-Exiles intro page does for you), or by paying extra attention at all times not to repeat.
The second is a true nuisance, but the only thing you can do is wait until you are sure the previous instruction you have issued has been processed before issuing the next one. This often involves a certain change within your playing window.
Assuming this was not an accident, you are well on your way to a suspension, most likely permanent, from the game.