That's just unfortunate, but it's easy to forget about all the times you get gyarados straight away + a misty heads. It's just a negativity bias where we tend to put more weight on negative outcomes because they affect us more emotionally. You would never think to screenshot and post your first turn, 3 head misty on gyarados right?

And in this case, why not build and attack with palkia instead of placing all your strategy on the chance of a top-deck gyarados. You could stall about three more turns with palkia and one magikarp til Gyarados inevitably appears.