Ineed coming up with a thesis statement that's about mercutio's death.

Okay. Let's think about this.
In the story, Mercutio dies at the hand of Tybalt. Mercutio tried to protect Romeo, and he got stabbed under Romeo's arm. What great luck.
To start your paragraph, maybe try something like this: "Imagine the person closest to you dies to protect you from intended harm. Mercutio, a bold friend, dies to save his good friend Romeo. Mercutio died because of three reasons-his pride, to save a friend, and to end a feud."
You take it from there, buddy!

If you give me the two excerpts to compare, i would be able to you : )