Channel Quilted Slippers

Right now, I'm trying (really hard) to work on my son's slippers that were started 2-4 years ago, and I'm finally decreasing for the toe. He saw the slipper model in a knitting shop and loved them, and of course it was supposed to be "easy" but both of us have had our own problems with it. He followed the directions, and knit about 1" or less, before wanting help, as he couldn't see the channels forming. We worked together, and then he gave up and I ended up starting them, knitting enough to see that the channels were forming, and a bit more. I don't think it's fun to knit, although it is an interesting design, and for some reason this project makes my hands tired, especially my left, so it was put aside for awhile.

Well, the other day he reminded me about these slippers, and said he would still like them, and luckily I managed to find where they had been stashed. Although the knit fabric looks ok, I'm wondering if I have knit so tightly that I've used up too much yarn, and will there be enough yarn to make two? I'm thinking that maybe I could make an educated guess, if I weigh the finished slipper and the remaining balls of yarn. If the yarn weighs less than the slipper, I'm in for trouble and will need to have my son try on the finished slipper to if he still likes it (for all I know he might not like the feel of those ridges under his feet).

I guess the worst case is that I go find new yarn and start over. I wish I lived closer to the shop that had the sample, as I could have gone there and looked at the sample as frequently as I needed to, maybe even worked on it a bit at the shop, they would know if I made a mistake, and I would have finished this the same year we started it, but I'll just have to figure it out on my own (this is what I usually end up doing, and I guess I haven't done too bad so far).