The correct answer here is to hold eye contact with her, smile, and then go up to her and say hello.
If you immediately look away, you come across as insecure, submissive, and unworthy of her.
Trying to create sexual tension by imagining having sex with her can backfire on you because it's too early for that still.
As for triangular gazing, you're probably too far away from her to make that even work, and it by itself would accomplish nothing if you don't go up and say hello to her.
The correct answer is to focus in on her eyes to most safely create sexual tension.
Looking at the girls entire face is not as connective or as intimate as looking her in the eye.
Looking her body up and down can also create sexual tension, but it's more risky than looking her in the eyes.
And looking at her breasts is even more risky- it's very easy for her to object or call you out on it.