I have used a few different ones of ready to print sheets, my favorite is the June Tailor, for ease of use and clarity of pictures. It comes in sew in, iron on, and I think a couple of other options. Yes it is a bit expensive but never a problem with it. I have gotten it at Hobby lobby with 40% off coupon. I had tried some from Walmart one time to see how it was.. I actually ended up throwing it all in the trash, simply because it ran and never could get pictures to stay.
Maybe it is the brand that you used and not so much how it was done..... Don't give up, they are neat to do and fun when they work.