In your example it should be "your *** is exactly the same as mine."
Interested in Language
Dictionaries don’t list “exact” as an adverb, but I often hear native speakers say “exact same”, like "your *** is the exact same as mine.”
Is this usage formally acceptable, or should I use “exactly” instead of “exact” in a formal situation?
Yes, but native speakers (at least my friends) use "exact same".
"Exact same" is tautologous even though you will hear it a lot. Something is either the same or it's not. If it's not the same, it might be "similar to" or "almost the same as" something else.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.