Take it to them assembled, and tell them it's too small and you want to return it. Bring the box and receipt. Hope this helps.
I would think it should not matter. They will have to take it back regardless. I had a car and it was put together and Walmart took it back.
The most important part of a return is the receipt. You could download the Wal-Mart app onto your smartphone, then load the receipt into it on your account, so that you can't lose or damage it.
I would return it Assemble just to show them how small it is, don't forget your receipt.
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