Dont take this the wrong way but I would omit both of those statements from your letter, TMI, you shouldn't tell your customer that your computer, at least in your opinion is not up to the task, it makes you look uncapable, and the bit about a creaform scanner, it sounds like you are telling him that the equipment you used is also not the best for the task, your casting doubt on your own work, less info is more in this case
I hope you can recover some of your costs at the very least, getting screwed on the odd job is inevitable if you have been in buisnes for a while, but it still sucks
Some customers are just never happy, you tell them at the start of the job "it will take two weeks", a week in your going for meetings to explain why your not done after one week, unrealistic expectations have become the norm these days