I think this bit is great. You expect some sort of huge romantic moment when Romeo and Juliet finally meet at the balcony. Actually, Juliet is terrified:
What man art thou that, thus bescreen'd in night,
So stumblest on my counsel?
She's terrified. She doesn't know who this man is, as he's covered by the darkness of night. She does know that he's stumbled on her admissions about being in love with Romeo (her "counsel" - her information). But then, when she realises it is Romeo, there is another fear altogether:
How cam'st thou hither, tell me, and wherefore?
The orchard walls are high and hard to climb,
And the place death, considering who thou art,
If any of my kinsmen find thee here.
She is terrified that Capulet's men will kill him if they discover him on their property. The Capulets and Montagues, remember, hold an "ancient grudge" against each other.
Hope it helps!