This happens to us all. When you cash out for the first time with an app, get your gift card in your email, and print it out. There is a small bit of anxiety when you use it for the first time at the store. Don't be afraid to use it. It is as good as a plastic one. I used a Walmart printed gift card, and the checker looked at me like I had a leg growing out of my neck. The gift card would not scan on the belt scanner. It made me feel like something was wrong with the card, so I got worried, then she used the hand scanner and it worked fine.
I felt like a weight was lifted off my shoulders, maybe it was the leg being removed from my neck. A lot of the gift cards do not expire. Be sure to read the details on your gift cards, so you don't have the same anxiety I did. A lot of the gift cards have codes, so you can use them in the store or online at a merchant website, like Amazon, Ebay, Best Buy, etc. If you have any questions let me know, and as always "fear not its only money".