Dell Inspiron 11-3168

Just received from Dell the other day. I plan to use it as a tablet. It says Windows 10 is not activated. I try to activate but it says words to the effect of, "your copy of Windows is not authentic. Please go to the Store and purchase Windows. Blah blah blah." A disc was not included in my box so I have no serial or product key. But I bought this directly from Dell, not eBay or a third-party seller. How do I prove to my laptop that I legally bought a laptop/tablet with Windows?