I've never heard "I made a boob" and I date back to the Bob Hope era. I have heard "I made a booboo", which is kind of an adult using a kidism, the next thing to baby talk slang. Someone who made a booboo could be a boob, however. Don't put it off on us as being American slang.
In fact, you guys are responsible for it. From dictionary.com:
boob1 /bub/ Show Spelled [boob] Show IPA Slang .
1. a stupid person; fool; dunce.
2. British . a blunder; mistake.
verb (used without object)
3. British . to blunder.