Sock update

Work on the celtic socks is progressing. I made it down to the heel on sock #1.

Everything went smoothly with the heel flap and the turning of the heel. It was when I got to the heel gusset small problems began to arise. When I had to pick up and knit 12 stitches along the side of heel flap on both sides, I found that the stitches I needed to pick up were very loose, thus creating a very loose, holey join. I'm not happy with this. What do you sock experts out there think? Did I do something wrong? Those stitches I had to pick up were slipped stitches, which is probably why they were looser. It's like that on both sides. I found that I can pull on the yarn and tighten it up some, which would be the less drastic solution.
Or I could frog back a bit and try again, but I'm not sure how much of a difference that will make unless I understand what went wrong. Also, I'm reluctant to frog back just yet, because there is a possibility I may have to frog a whole lot of it soon if I run out of yarn. The pattern calls for three 50 gram skeins. When I was buying the yarn, the woman selling the yarn generously told me that she found that only 2 skeins were necessary. She had smaller feet than I have, but I figured I could just make the sock leg a bit shorter. But when it came to it, I decided not to make it shorter because 50 grams should be plenty for 1 sock, right? I've knit socks for myself before that used less than 50 grams per sock. But now I'm starting to worry just a tiny bit....