no you didn't waste time because it helped you to get some money you needed. now if there was a way to cap it at, say 200, and then spend 100 on another craft, you could still do well to make money even with 200 skinning skill.
having said that, as you get higher level, the things you did as a level 10-20 character to make money might need to change. eg as a first-timer with a low-level character, i much prefer to sell linen and wool and silk to make money. as i get higher level or i play an alt, i might now use those to work on first aid skill since my main character is now established with his routine.
not to mention, my high level could farm those items easily and send to my alt..or use a friend/guild members to do a free transfer.
so dont feel bad that your need for other money-making methods now causes you to change. since you got it ot 300, you apparently can survive in the zones that are needed to increase skinning skill. in the worst case, if you decide to re-skill it, it could be as easy as skinning 300 monsters since this game gives skill-ups so easily.