This is actually a popular sentence in American slang, "He's not bout to give it back". (If you're trying to use slang, skip the "a" in about) If I'm "about to" eat that means I'm going to do it very soon. If someone asked "What are you doing right now?" A valid/typical answer would be "Im about to go get some dinner". For your context, it's not an incorrect sentence and a native speaker can say it without people noticing, but most people would say it "He's not going to give it back" OR "He probably wont be giving it back" OR "I'll probably not be getting that back".