Take a deep breath, and keep going. I completed an auction quilt top a few years ago, hung it up so I could take a picture of it and realized that the background fabric I used was two different dye lots!!! I asked fellow staff members what they thought I should do, and they said, "Leave it as it is." There wasn't a huge difference between the dye lots, but I knew it was there! It formed almost a straight line across the bottom third of the quilt top!! I had done so much work on it already that there was no way I was going to leave it as is. So.....I took a deep breath, and had to take it all apart because I couldn't find the matching dye lot that matched the top 2/3 of the top!! I went to every JoAnn's in town!! Basically, I made that doggone quilt top twice!!! When I was finished the second time, I was glad I decided to rip it all apart and redo it. I know it's a pain in the behind, but in the long run it is worth it.
Try to figure out where you keep making your mistake(s), and perhaps make one sample block that you can use as a reference. Before sewing on the next strip, take a look at the sample.
Good luck. Be sure to post a pic when you're finished. I'm sure it will turn out to be beautiful!! :thumbup: