No need to convert it. When you ask the authorities to put your name as a resident in the blue book, they will automatically give you a yellow one, the blue one is reserved for Thai national names only.
Strange they haven't checked the copy of the visa carefully, or maybe it doesn't matter to them that you misclicked as soon as they got the right insurance etc.
If you come back before end of August you can still keep your allowed stay with a re-entry visa to get before leaving Thailand. Then you'll ask for an extension when you're back.