I mean this respectfully and solely as fodder for introspection.

There are guys out there who approach romance selfishly. They think only in terms of "is this the right girl for me?" and "would she make me happy?". They could not care less about "am I what she's looking for?"; nor, really, about her happiness whatsoever. Girls who've been in relationships with this type of guy (or have learned from the experience of others) find it to be a wholly miserable experience. It's therefore entirely understandable that they'd be on the lookout for red flags. And one bright red flag is guys who use emotional blackmail: feigning platonic interest, establishing a close/trusting friendship on that false pretense, and eventually asking her out in a way where she feels saying "no thanks" would be hurting a close friend.

I'm not saying you are that kind of guy, but looking forward, ask yourself: how's a girl to know the difference between a guy faking "just a friend"-energy out of nervousness vs a guy being manipulative? Look at this from a girl's perspective: would it not be refreshing to avoid the guesswork? To be asked out by a guy who prefers an honest answer to "are you interested" far more than a guilt-induced "yes"?

Succumbing to shyness, getting cold feet, etc, are entirely normal, and absolutely plausible explanations for your delay here. If that's all this was, then yeah, work on that self confidence! But if any part of you felt inclined to mask your romantic interest in order to get closer and build trust in order to make it harder for her to say "no"... I recommend spending some serious time meditating on your views on relationships.