My childhood friend finally agreed to meet up but her reply was short so is it a bad?

If she's not very active online, why not get a phone number to arrange things more quickly?

However, it's concerning that you talk about asking a friend for coffee, then jump to being rejected and dates and girlfriends. What exactly are you hoping to gain from meeting someone from 12 years ago? Is it a catch-up or a date?

I wanna fall in love with her. In fact I am already in love with her. I want her as my girlfriend.

When was the last time you actually spoke with (not messaged) her? Does she know it's a date and what your intentions are? It's all sounding very one-sided and you're more likely to scare her away by being this intense.

2011 was the last time we spoke in person. My parents bought a new apartment that year so we came to another area of our city. We were in the same school during high school too but didn't interact as we weren’t in the same class

So there's a young woman you were friends with for 3 years when you were kids, you couldn't be bothered to make an effort with her after the age of 10 and haven't spoken with in 12 years. And you want her to be your girlfriend? Riiiiight....

If this isn't trolling, it's immature and desperate. Cancel the coffee and grow up.