It depends which country you live in..
In a country like the uk, you can just deny you ordered it, that it was a wrong order or that they must have sent it to the wrong address.
You can always say that you were going to try meat curing, and that you were unaware it was a restricted substance.
If it comes to it, you can always come clean and say that you were suicidal and bought it on impulse, but that you now realise your mistake or something
I'm not sure there's much that can be done to you legally. It may be restricted but it's not illegal to possess. I think