For hiding those edges or the occasional missed stitch, don't waste a lot of money on expensive fabric markers when you can use Sharpie permanent markers instead! Points to consider:
* They're more readily available
* They come in a huge assortment of colors
* They can be had in various thicknesses
* They're very affordable
* They're permanent
* THEY WORK!
One thing that has always bothered me is spending dollars when you don't have to. So what to do? Improvise...yes, sometimes we need to spend extra or more dollars for some things to get a certain quality, but from personal, long term experience, I have found that for filling in the occasional missed stitch or design edge that didn't quite get to that outline for whatever reason, Sharpie's do the trick. You can get them in fine to thick, I suggest getting as many as you can afford, you will definitely need fine for the tinier areas though, so if you can only get one set, get the fine set.
They're permanent and if you are really worried about using them, practice on something first, while remaining aware that different textiles will 'wick' the ink differently (suggestion: practice on a scrap) and make sure you're calm and your hands are steady. Feel free to heat set with an iron (remember to protect your iron plate) by using a pressing cloth or heat cloth.
Save your expensive fabric markers for larger painted areas