Hi,
I’m following the tutorial and I’m referring to 5:16 in the video.
When the instructor adds the Mirror modifier, his result looks correct.
Instructor’s result:
My result:
I followed the exact same steps, but my result looks different.
Did I do something wrong?
The issue is your origin point. See how the middle yellow dot in Chris's screenshot is in the center of the world. In your case the model is to the right of the world origin.
You can watch the mirror modifier lesson in this course if you want further deep dive:
https://cgcookie.mavenseed.com/lessons/lesson-8-mirror-modifier