Depending on the context, "turn up" means to "increase". e.g. please turn up the lights. to "show up, appear etc". e.g. the evidence turned up by themselves; the guests failed to turn up on time. "turn out" means "prove to be the case" The prince turned up to be a fake. "eventuate, happen, develop, occur" Things didn't turn out to be expected. "become clear, emerge, become apparent" It turns out that she was not at home. "go somewhere for something" some of us turned out to vote on a rainy day. You didn't turn out to be a good friend is CORRECT. Using turn up is WRONG. In your first example, the correct sentence should be, "if you're making a cake and you don't follow the recipe, it doesn't really turn up GOOD"

"Turn up" usually means something appeared physically. "Turn out" means that something happened as you expected. Therefore, the cake didn't really become what you thought it would be. Other examples: "My sister turned up for my birthday." This means that she was able to attend the birthday party. "My project didn't turn out well." This means that the outcome of my project isn't what I thought it would me.

Thank you, Victoria Hill :)

turn up can be slang for a party turn out means more like results you seemed like a good find but turns out you're a bad friend