Was pressured into signing a warning slip because my till was short today, I need help/advice!

So I made a huge mistake and I didn’t know any better. I let my manager pressure me into to signing a warning letter, then a family member told me I made a huge mistake doing that.

Here’s the context

I recently started working at Cane’s and I found out a manager I worked with in the past is working there also. This wasn’t good to hear because we didn’t leave each other on the best terms. At my last job, this manager (let’s name him “Joe”,) basically thought that I was a thief because every time I worked a shift with him it was always short a few hundred dollars. Because of that, we didn’t get along. He would always threaten to fire me because of the missing money. We didn’t get along. About 3 months into my job, after being constantly accused of theft, I found out that my job finally caught who the thief that was stealing out of my cash till. I also found out that Joe was fired both because he giving his family food from the restaurant without paying and because whoever the thief was accused Joe of attempting to search me and a few others. So Joe got fired. Couple of months past and he apologized to me for the situation.

Fast forward to this year and we’re both working together again.

About a week ago, Joe said that my till was short $14. I was confused because it was pretty much a slow day and I am very exact when it comes to counting change. So, when Joe asked how could this have happened I genuinely couldn’t give an answer/explanation.

Fast forward today and he brought up about my cash till being short last time, he said that I needed to sign this warning slip. I was so nervous and scared so I gave in and signed it and now I realized it was a big mistake doing so because that basically meant I’m taking responsibility for this. I’ve been in the payment station a few other times and none of the manager have ever told me my till was short, just Joe. This happened at the last job I work at with Joe in. None of the managers had troubles with my till, just Joe. I’m scared more will come from this because I’m realizing that Joe may not be as honest. When I told a family member, they told me that typically managers count the cash till in front of you which Joe did not do. They also took note of how odd it was that Joe kept pressuring me to sign the warning slip (that I *stupidly* did end up signing because I thought I had no choice to do) how Joe would constantly try to shorten my shifts and constantly *made* me feel like I needed to do something that I didn’t have to do and a lot of other shady things he does.

What can I do to combat this? Should I take it up with HR? Should I talk to the store manager? What do I need to do?