Can a collarbone with hairline fracture (landed on it while skiing downhill) heal incorrectly? have a bump where it broke then can't feel rest of it.

Probably not: If it displaced a little and healed with some displacement there can be a bump. Also if there was callus you can feel that as a bump as well. Although u would usually be able to feel the other side were that the case. Clavicle fractures do well if they heal with non operative care. There is some evidence that very displaced fractures can result in some strength loss if not fixed.

On rare occasion : Clavicle fracture tend to heal very well. The callus formed creates a bump that molds over time. If there is no pain or limitation of movement, no worries.

Callus: The bump is called a bony callus, and is a normal part of the healing process. Assuming you don't have a displaced fracture, it's likely you'll have no long-term deformity there.