Needle valve connection to plastic tubing
Your assembly looks right. The tubing could be nicked, though, so when you try again snip off an inch from the end of the tubing so you'll have a fresh surface to work with. Also verify the mating face of the valve is clean and undamaged.

One common cause of leaks with poly tubing (at least it used to be for me) with the use of a brass ferrule is that the ferrule can get misaligned a little too much. It gets compressed a little out of round and won't seal. It's more prone to happening with poly tubing because poly is softer than copper tubing. The job definitely can be done with a brass ferrule; I'm only saying it can be a little challenging and don't feel badly that it has taken a few tries.

You could try the connection with a Delrin (aka acetal or "plastic") ferrule as illustrated in this answer. They're a bit easier to work with on poly tubing. These ferrules are generally available alongside the other fittings for tubing in a plumbing department.