Here's another tutorial on a different style of postcard- this one is the faux quilted look.
Mine isn't perfect, because nothing I make is- but the video includes a few tips to help yours look closer to perfect (if that matters to you). The number one hint is to measure you fabric, something I didn't do, and to pay more careful attention to where you are stitching.
I like a quick and easy project more than I like a perfect product most of the time. As long as you aren't looking super close up like the camera is, I think this looks pretty good!