Step 1: Screenshot your schedule from that day, as well as any snaps or photos you may have taken on shift near or at the time you clocked out (to prove you were there). Screenshot the time adjustment as well.
Step 2: (*ONLY if you feel comfortable. Skip if not*) Mention it to your SM and ask what the hell? Ask for a readjustment in your favor. If they say no or pretend it didn't happen, ignore them, play it off, and get ready to move up the ladder. This was only a courtesy to your SM because you have to see their face at work often, and they have direct means to fuck with your job status. Don't press it. Don't argue. They're digging their own grave at this point and will not last much longer at the bux after you get to the next steps.
Step 3: Contact the Partner Contact Center. Tell them you have a payroll issue and that you'd like to speak to someone internally. This is important verbiage to use: "Before I call the Department of Labor, I was hoping we could figure out this problem internally to get me adequately paid for my time on the clock." They likely won't protest and will fix your problem from here to save their own asses, but let's pretend they do give you a hard time. What would you do next?
Step 4: Contact 3-5 lawyers near you. It is important to ask for someone that can help you with a labor dispute, and that you're looking to make a formal complaint to the US Dept of Labor. Many lawyers love these cases because they know there will be a payout, especially when the client has receipts (screenshots from step 1). Pick the lawyer that is willing to work on contingency. This means the lawyer service will be free for you because the lawyer would be paid out of your winnings. If you make it to this step, consider asking for payment for this time it's taken you to consult Reddit, call lawyers, and deal with something that shouldn't have happened to you. Consider "pain and suffering" as well, because retaliation is a realistic expectation to prepare for.
Step 5: Listen to the lawyer from here. Things vary state by state, and this is as far as my knowledge goes on the subject.
Step 6: If you're willing, able, and ready, you can start working towards unionizing your store!
$1 is a nice link about how to get started with this if you're interested. Together, we bargain. Divided, we beg.
I'm sorry this happened to you. I hope it works out!