"Play it as it lays" is a poker expression.
When you are playing poker with wild cards, and you show your cards at the end of a hand, it is possible to have a hand that can be interpreted in more than one way, because wild cards are by nature ambiguous. House rules, i.e. the rules of the game that is being played, can either say that the hand is what you call it, or you play it as it lays: it is the strongest hand that can be built irrespective of what the player to whom the hand belongs calls it.
I have a hand with 3 wild cards, and a Jack of Diamonds and an Ace of Spades.
My opponent has a flush in Clubs.
Now, let's say that I CALL my hand a straight with one wild card being a 10, a "natural" Jack, another wild card being a Queen, the third wild card being a King, and then the natural Ace Of Spades: then I lose to the flush in Clubs.
But when I lay my cards on the table (see what I did there?), someone else says, "You know, with the Ace of Spades and three wild cards, you can also say that you have 4 aces - and four aces will beat a flush."
Now, again, my hand here is ambiguous: it's either a straight, or four aces. Some games operate under the principle that once I call this hand a straight, it is and remains a straight. OTHER games operate under the principle that if I call it a straight, but it can also be interpreted as four aces, then it is four aces, irrespective of what I called it.
So in the given example, under the rule that says the hand is what I call it, I would lose; but if the game says you "play it as it lays" then then I would win - even if I did not initially realize it.