You can pay inside instead of using the machine. But the code you're supposed to you is all the way at the bottom of your receipt, and easy to miss.
The washing machine doesn't touch your car, so you can be sure it's not adding swirls to your paint. But even with the higher tier washes, it's simply not enough to get heavy dirt that's had a chance to sit on your car for a long time. I recommend just getting their basic wash, right before you find time to properly hand wash yourself.