It happens to me too. I have found that when I am auditioning things and trying to visualize what it will look like, I don't always get it totally right. I then need to make a quick adjustment, just like what you described. I like it. That is when the quilting process gets interesting to me, when quilts don't want to use the fabrics you have selected for them and they move to you find another...
I agree with Deemail above. She is absolutely right about her fabrics. Deemail the overall design is lovely!