Pregnant Snooki -- The Ultrasound's LYING ... I'm Still a Polizzi

Snooki did NOT secretly get married to her baby daddy Jionni LaValle ... and she did NOT secretly take the guy's name either -- despite what her ultrasound says -- sources tell TMZ.

In case you missed Thursday night's episode of "Snooki & Jwoww" -- the Snookster unveiled her highly-anticipated ultrasound ... and Snooki's name is listed as "Nicole LaValle."

But Snooki sources tell TMZ, the ultrasound is WRONG -- because Snooki's real name is still legally "Nicole Polizzi." The doctor's office simply entered the wrong name by accident.

And for all you conspiracy theorists -- the source adds, "Snooki is 100% not married ... yet."