Svend consider yourself lucky; you took the lowest bid and you will still come out on top whether you give the kid a bonus or not. In the past when I have lost out to the lowest bidder, more times than not the consumer will call me back with a horror story and literally beg for some assistance or advice on the matter....I'm sure Tboy has experienced the same. Usually the lowest bidder doesn't have a clue what they are doing, in your case it sounds like more of a lack of experience than talent. Like I said you got lucky. The ones that overcharge are guys that are so busy that they can afford to take a chance on a sucker...I'm sure that Tboy has been there at one time or an other, I know I have.
I say give the kid a few few extra bucks when he is done, and a small lecture. As others have already said, it will pay off in the future; not because of Karma lol but because you will have a loyal and talented trade at your disposal, which is becoming harder to find these days.