Take a hat I just finished. It is soft, lovely, but too large. I mean, it should not cover one's eyebrows (sigh). Finally, after looking at it for two days, I managed a solution. I had two matching little yarn loomed-flowers of the right colors. I got these (Bloomin' Blossoms) from April on her former Etsy store. Her new shop does not show these but I'm sure she'd be happy to show you what they look like. Anyhow, I put one on each side of the hat. I pulled the trailing yarn pieces through stitches on both the body of the hat and the fold up brim, spanning 3 stitches for each flower, and tied them on the wrong side of the hat, and tried it on. Wow, improvement here, but not enough. So I went back into the wrong side of the hat, and because I still had enough yarn left, I pulled the tails through two more stitches on each side of the flowers (five stitches "gathered up" on each side. That seemed to do it. I tied them off and tucked the tails in. The hat looks cute with them on, plus it is now a much snugger fit.
Taking something in a few stitches here and there usually isn't a big problem. I know most of you have probably done something similar a million times.
However, when something is too small, I still cannot figure out how to deal with it except to rip it out and start over. I really must get into the routine of making a test swatch to check the gauge.