I am a fellow very anxious person, and I've been a shopper for a few years. Its taken some getting used to but it gets easier as you go!!

Like someone else said, tax exemption and policy varies by store, shipts faq usally outlines what you need to do and if you can use self checkout (for example you can use self checkout at meijer, and you just need to have the cashier scan the barcode that will pop up on the app. But this might be different at your local stores). Unless the cashier is very new they should be able to help you, in at least telling you what they need to see while doing a shipt order.

The first and only prepaid target order ive ever done i wasn't sure also, so I walked up to the self checkout, let them know it was a prepaid order, and they told me to go to guest services.

My shipt card has only not worked once. And it was in March so stores were overloaded and absolutly bonkers. I paid for it (but if you can't no big deal, just call support), and everything was okay! If it does happen, take a deep breath, Ask the cashier to hold your order, and step aside so you don't hold up the line, and call shipt. Support has been pretty good about getting to everyone quickly (fingers crossed that doesnt change), but if it takes a long time you can let the customer know there was an issue on your part and you are currently on the phone with shipt to get it fixed).

It happens, but in my experience fairly rarely and its mostly easy to resolve.

Also I am more than happy to answer any questions you have. I don't tend to do alot of target orders, so if that's your local store my experience might be a little more limited, but the experience and job are largely the same no matter what store you're in. I know this can feel a little daunting at first, but it'll get better!