For me personally the best bet is to say to a girl that I like her after spending just a couple of minutes to at most hours with her.
Obviously I need to have some strong IOIs, which shouldn't be a problem after that time.
The thing that happens when I clearly state my intent (
note that it must be clear to her! "I like you" may not actually be enough!), I feel free to actually behave normally. I took the risk of being rejected by her, and that alone is attractive for a woman that has at least some interest in me.
I then proceed to express my feelings in a
non needy way!
I say things like "You know I love you" with a
playful attitude. She is never truly sure if I mean it. When she says something like "I like you too but only as a friend", I reply by something along the "Well I know you are a girl for me. It's just a matter of time when you realize it as well..

" - again
playfully!
The playful tone of voice and your expressions makes her uncertain which in turn makes her to think about you more. Then I escalate physically but never beyond what she feels as really uncomfortable. No attempt to kiss her, if she is uncomfortable with me playing with her hand etc..
In your case, I would just keep on going. Keep it light though! No needy "I need you" or "My life without you is meaningless" kind of shit!
Be happy around her, tell jokes, stories from your life etc. but not to entertain her, but rather amuse yourself! Emotions are contagious! If she feels happy around you, she will be more attracted to you. And from time to time you can remind her that you love her, but in a completely
non-reactive non-needy way!