Cannot enter Ace of spades giveaways.

Hello. I've been playing Ace of spades when it had it's free weekend and the game was kinda fun so i deciced to check if it had giveaways of it on here but to my suprise when i was about to enter one it said i already had the game and that's why i cannot enter the giveaway? That's strange because the free weekend of the game ended ages ago and the game it self got removed on my steam gameing list. So my question is, is it a way to fix this or am i doomed to not being able to enter giveaways of the game?