In Act 2 of Romeo and Juliet, why does Juliet fear that Romeo will think she is "too quickly won" ?
Hmmm, I never thought that Juliet actually "feared" Romeo's thoughts about that subject. Juliet knows that Romeo is already in love with her. For goodness sake, he has been spying on her even under penalty of death! Juliet is simply flirting with Romeo here and, I believe, jokingly makes that comment. Let's review the context, though, just for clarification:
Oh gentle Romeo, / If thou dost love, pronounce it faithfully. / Or if thou thinkst I am too quickly won, / I'll frown, and be perverse, and say thee nay, / So thou wilt woo; but else, not for the world. (2.2.98-102)
You see, obviously Juliet has already given Romeo the "go ahead" in this case. She is joking about propriety here: what is usually done in her time period. Usually men "woo" women: spend time courting them and winning their love. It's the equivalent of Juliet saying something like, "Okay, if playing hard to get is what you want, then I'll give it to you." She clarifies her comment at the end of the quote above by saying that, unless he tells her otherwise, Juliet would never tell Romeo "no."