Fell in love with a younger girl

Hello!

I am an international student in Canada, 28 years old, approached a girl on the street near the university and got her number. First date was quiet nice, she always smiled, laughed at all my jokes, however she seems to generally laugh easily. At the end of our date I hugged her in the cheek.
Well there were some negatives which I can remember now:
- I mentioned that I got a tendon inflammation and can't do sports
- She is 18 and I am 28, even though I feel and look 22, as he also said herself. When she asked me at the beginning of the date how old I was and I honestly answered, she said "Oh, I didn't know that". Yeah, and during the dates she several times half-jokingly mentioned that I was old, where as I always emphasized how young I am; and when I just wondered that she was going to study medicine for 8 years she made it clear, that nevertheless when she graduate she will be still younger that I am now.
- She is Canadian and I am not(however I mentioned that when I approached her).
A remarkable positive was that she told that she believes in and follows horoscopes. She asked me and I said, that I don't follow them. By the way she asked me that after asked me my birthday and after figuring out that we are the same. Yeah, I said that I don't follow that stuff and she said that she does and emphasized that we are the same sign.
What I have to mention else is that I didn't touch her during the date at all. It was in a tee house. We just drank tee with a cake and then went for a walk along the harbour for a little bit (by the way another positive thing is that when we began to go for a walk I asked her if she didn't feel cold and she said that she did, then I suggested to go back and she said "no no, it's ok", I asked "You sure", she: "Yeah, I am sure").
Yeah, what can I say else. I fell in love with her and am thinking about her all the time and can't really study, my heart beats fast all the time and I've got a chest pain since after my text with asking your on a first day she refused.

I text her 2 days after our first day: "Hello ..., How have you been? Today after class, I'd like to go for a walk with you in the Green Garden for an hour or so. Are you free after 6:30?"

She answered "Hi..., I am supposed to meet some of my friends later this evening so I won't be able to! I am sorry".

Well, What I think myself: It can be true, but as I feel, if she would like to meet me again, she wouldn't just say "I am sorry", but suggest another time or so, or at least text me next day, but not...

So, what could you say? I would be very grateful for any tips, also for future as I am aware that I totally failed with this girl and have to suffer for a while, even though I'm not sure that it will be that simple, as I really fell in love with her... When I should fight for her... then how??? How could I correct my mistakes?
Please also fell free to ask about details of the first date.

PS: I haven't used any pick up techniques. I am anything but familiar with that.

Thanks a lot for your help in advance!!!!!!!!!!!!!!!!!