Ex girlfriend cancelled our date

After being apart for 9 months we have started seeing each other again. She hasn't said it yet, but it's clear to me that she's still in love with me. But part of me senses she is unsure about getting back together again officially. She's just being sensible there, I guess.

I texted her on Wednesday saying I missed her and we arranged our 3rd date for this weekend. She said she was excited so I was surprised when I texted her today and she replied saying she couldn't make it and had other plans.

I've probably brought this on myself because I didn't respond to her text on Wednesday confirming where and when... So I guess not texting her for 2 days and playing hard to get backfired :/

Why do you think she has cancelled? What reasons could there be? I honestly don't think she is interested in any other guy because she told me she hasn't been with anyone else since me, and I believe her on that 100%