Hmm, I don't think you need to start over! I haven't got experience but I would recommend using less water to stick them down with and wait for it to dry, that's when it's the stickiest, if that doesn't work then use some watered down PVA glue and slide it into place then once dry mod podge over, please be careful the glue doesn't take off the design though, if you can test it first that might work.
Hope this helps x