This is very nearly off topic, but "Ain't" is the correct conjugation to pair with "Gonna". This form comes from Britain and is preserved in some dialects of American English, but "Aren't Gonna" is a partial hypercorrection; if we want acrolect, we must go all the way to "Aren't Going To".

"You gonna be at the thing this weekend?"

"Nah man I aren't gonna" <-- this is wrong

For the Commonweath, to whom this is no longer part of the language, "You Aren't Going to Need It" is fine, no need to include the T.

Edit: I was drawing further attention to the actual grammatical distinction between "ain't" and "aren't" by showing that "ain't" conjugates the first person and "aren't" doesn't.

It might help to know that "going to" is usually pronounced "gonna" unless it ends a clause, while "gonna" is more normally realized in speech as "goan".

Even more: if you want to reify a partial hypercorrection, go ahead, I'm a descriptive linguist, say the 't' in often while you're at it.

One of my grandfathers would have said something sounding like "yain go need it", the other "you aren't goin a need it".

The latter I'm sure never said the word "ain't" in his life. Nor would he have ever spelled "going to" as "gonna", no matter what it sounds like when spoken.