(Note: “Locs” is a word exclusively used to describe the locked hair those whose racial heritage includes African ancestry.)
You should be able to safely and gently brush that out. You really shouldn’t have to cut it off. Check our removal tag for more information. You can pretty much brush out/detangle any form of locked hair unless it’s been glued together or some other horrid idea.
Remember that your locks will thicken with time and at only 3 weeks you won’t be able to see the full thickness just yet. They will likely thicken substantially between 3 and 6 months for most people. It happens a bit sooner if you have kinky/coily hair, and a bit slower if you have straight/wavy hair.
You can always combine your locks later on, or brush them out and start again. The number of locks on your head doesn’t define how thick they’ll eventually be necessarily. This can vary drastically from person to person. If they aren’t thickening up to your liking around the 6 month mark, try combining some or brushing some thin ones out to make them thicker.
Also, be a bit hands off with maintenance- crochet hooking tends to keep locks thinner, for example. Be sure to separate daily- especially the back of your head!