What does it mean when a girl doesn't text you back?

Ok so I went downtown last week and as I was leaving the bars, I saw this gorgeous girl. We made eye contact and she smiled so I went over and talked to her. We exchanged numbers and I texted her the next night. It went really well and she responeded to my texts fairly quickly. I asked her to have dinner with me on friday which she replies with a smiley face and said she would be glad to join. After our conversation, I decided to not text her the next day so I don't seem to eager but I texted her again two days after. We talked again and it went well but we had delayed conversations since I was busy and she was busy too. Then she didn't text back to one of my text so I decided to just text her the next day. She didn't reply again and I didn't want to smother her but I texted her on friday since we were suppose to have dinner. Again, no reply. Normally I'm really good with girls but I don't know what this means!! Help me what should I do and what does this mean?