You can use a nail file to gently smooth the ends of his toenails so they don't snag as easily. If they're quite long, you can carefully snip very tips with fingernail clippers first.
I found paper towels on top of an inch or two of pine shavings, or just the shavings themselves, to provide a good walking surface.
The big problem with splayed leg condition is that the chick's brain has decided that pushing the leg to the side is the most effective way to use it.
I'm afraid that at 3 weeks, it may be too difficult to reprogram. If the chick has developed its muscles a lot for turning out to the side, putting hobbles on it seems to just reinforce its continuing to push out rather than trying new angles--The chick learns to stand based on pushing the one leg to the side and the splayed leg's tension against the hobble (which is tied to the stable, standing leg) being used for balance. Then, the chick can become
reliant on the hobble for functioning, rather than the hobble helping motivate the chick to explore options and retrain its brain.
If a chick continues to wear
and rely on hobbles for an extended period of weeks, its leg will become progressively more deformed. I know--I nursed one for 5 months that way...
You'll have to analyze whether the chick seems still capable of perceiving that forward (vs. sideways) leg movement can be a beneficial way to stand and walk. I'd think the way to evaluate would be doing physical therapy and observing how apt the chick is to try out doing correct movements as you help it.
If the chick seems able still to experiment and explore, you'd probably need to do frequent (8-14 times per day for 1-5 mins.) physical therapy for a few days. At this stage, I'd recommend keeping the chick confined to a small area so it doesn't spend much time trying on its own to use its previously learned, incorrect movements. If it gets better enough at moving its legs correctly, you can start taking the hobbles off for short periods of time, increasing the amount gradually.
So sorry for your trouble. So hard! Best wishes