I did something similiar. Even though most of paint I used (i didnt realize mistake until on wall)-exchange was no hassel, very easy
They are open mind about returns. But if you used it just a little your return and change will be easy....
Good luck
You can bring the paint back to the store, explain your situation, and they will work with you on how to resolve the issue.
If you haven't used the paint for your back they should exchange it for you
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