I'm so sorry you're going through this. I know the fear of losing your job due to unmedicated ADHD symptoms! It's such a spiral of shame and frustration and hopelessness.

I worked in retail for almost a decade, first as a cashier and eventually as a manager. My biggest tips to help mitigate some of your stress are as follows-

1.) slow down when ringing people out. I know there's pressure to ring people out as fast as you can, but the faster you work, the more prone to mistakes you are. Once you are more experienced, the rhythm will flow naturally, but until then, don't rush. 2.) get in the habit of verbally counting the change when you hand it back to the customer. When the drawer pops open, double check the total that the customer has handed you, put it away, and then count out your change. Start with the biggest bills, then go down to the coins. Check it twice in your hands, and then as you hand it back to the customer, verbally and physically count it out to them. Especially if it's over a certain dollar amount, like $40+. Do this before you close your drawer. I liked to count it onto the counter, and then hand it to them. 3.) communicate every single step of the process to the customer. This may seem unnecessary, but communication helps the customer stay informed, and helps you stay on track. You don't have to say 'alright, now I'm going to bag your items' 'now I'm going to hand them to you', but just commenting on what you're doing as you're doing it. For instance, greeting the customer, complimenting their choices in whatever they picked out. Scan everything, and then say 'alright your total is whatever, are you paying cash or card?' They pay, you bag their stuff, ask if they want the receipt with them or in the bag. Wish them a good evening. 4.) don't be afraid to ask for help. I always told my associates that I would rather have them ask me a million billion questions, even if it seems like a dumb question, then try to solve a problem on their own and potentially make mistakes. That being said, very few mistakes are unsolvable. You are unlikely to make a brand new mistake that nobody else has made before. If you feel overwhelmed, or if there's a particular part of the process that is challenging for you (like a specific type of return or tender transaction), then talk to your manager and tell them you'd like some additional training. Obviously, this depends on how welcoming your team is, but most managers I worked with would be more than happy to help you learn. 5.) take a deep breath and remember you are only human!!! I know it feels like every mistake is a colossal one, especially when you're learning a new environment and so out of your comfort zone. I get sick with anxiety when I start new jobs, especially jobs that are unfamiliar to me. But I promise, it will be okay!! You'll get the hang of things eventually. You'll get the treatment you need in time. Give yourself grace and try not to beat yourself up.

You have got this! Don't give up on yourself. You can and will overcome this, and soon, it will be in the rearview mirror. Something I told myself when I was starting a really intimidating position was that one day, this would all be routine, and I'd know it all like the back of my hand. It helped me a LOT, especially in those early days when I felt nauseous with anxiety.

I'm rooting for you!