Returning a baby car seat to Walmart without a receipt?

Gabriela • First time mom. 23. Due 06.26.17
Does anyone know if I can return it without a receipt? 
My uncle bought me 2 months ago a Graco Snugride 22 car seat and stroller.
Unfortunately when I took it to the police to have it inspected, they said it isn't an easy car seat and that I would have to be adjusting the harness from the back all the time instead of the front. 
Now, the issue is I don't have the box where it came in and I don't have a receipt and my uncle paid in cash.
So what could I do??
I would really like to exchange the seat at least for a safer and better one. I am a FTM.
Thanks!
Also if anyone knows if the Graco Snugride 22 car seat base fits a Graco Snugride 33.?

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