In Romeo and Juliet, what does her placing the dagger beside herelf as she drinks the potion signify?

She talks to the dagger, and says

What if this mixture do not work at all?
Shall I be married then to-morrow morning?
No, no: this shall forbid it: lie thou there.

She goes on to wonder if she's going to be in the vault before Romeo arrives, if the friar has poisoned her, if it is a trick so that she will marry Paris... and Paris is totally not what she wants. If the potion does not work, she is willing to commit suicide to prevent this marriage.

I think this moment is symbolic with the dagger because it foreshadows an upcoming situation. Keep that dagger in the back of your head.