“Not knowing” ; Why not зделая but сделав?
“Not knowing” is a very bad translation. делать ошибки means “to make mistakes”. Делая would be a present gerund (making), whereas сделав is a perfective past gerund (having made): сделав тысячу ошибок having made a thousand mistakes.
More info here:
http://russianlearn.com/grammar/category/gerunds
[Edit] Notice that there’s no present pefrective so сделая does not exist