I amended my tax return for 2016. I sent my documents in and I still received my refund. Does it need to be returned back to IRS? Or did I make a mistake?

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No, the refund you received from your original return does not need to be returned because you amended your return.

If you expect to receive a refund from your amended return, it is in addition to your original refund.  

** The amendment Form 1040X will be ready in mid-February. 

Amendments need to be printed, signed, and mailed when completed.   

See FAQ below on returning your refund after amending: 

https://ttlc.intuit.com/replies/4642225