"I have a boyfriend" often means you a telegraphing too much interest too soon. If you are going indirect then remember to have your body language face away, open over the shoulder and only turn your body language towards her as the conversation progresses.
As for flaking, make sure you have established some kind of connection with her and have a legitimate reason to see each other. It can be as simple as showing her your favourite café or her joining you and your friends at a club night your friend DJs at. You don't have to actually do that specific thing, but future projecting makes her invest more in your interaction and she is more likely to remember you. Also try and set up day 2s on weekday evenings because it's less pressure than a weekend invite which can feel more like a "date" and also she might be worried she'll have to spend all of saturday night with you rather than her friends, and you might actually suck balls.
Finally, before sending out an invite, send a random and/or funny message that doesn't need a response a few days after meeting her. My outbox is full of messages that just say "omg I just met your twin!" It's a great message because it's random and makes her imagine tons of possible situations, makes her a little bit jealous, and shows that you're out meeting other women. THEN when she gets back to you, throw out the invite.
The invite itself should be to something a bit more interesting then dinner or film. Be aware of whats going on in your local area and in your town/city in general. You'll get points for knowing the new hip tapas place that just opened up, the underground indie place with free shows on weekdays, or the quaint little shop that does wine and cheese tasting every wednesday. Bounce to a few different locations, the last one of which should be walking distance to your house. Hopefully I need not spell out what you do then
