I think it is correct but you should write I am doing an amazing and then you complete for examnple I am doing an amazing job or work just add an

The sentence seems right but you need to have something on the end. For example, I am doing amazing work. You could just say though, I am doing amazingly.

Adjectives used for adverbs is common enough in very colloquial English, as in the laidback atmosphere of a podcast (and I wouldn't call it "slang"). However, it is considered substandard in writing and in most spoken contexts, which is why you were corrected by a native in your notebook entry. Because you are a non-native speaker, people will automatically assume not that you are flouting the "rules", but that you haven't internalized the rules properly, and until you prove a certain degree of proficiency in all registers of English, people will continue to correct this as "wrong" (and even after that). And since the object of the game is to communicate effectively, get what you want, and not elicit adverse reactions from people, you are better off avoiding this type of usge, at least for now, and secretly (with an "-ly" :) ) delight the informal "edginess" of the podcast you enjoy.