Not that this isn't frustrating but the more you practice and learn how to match your seams there will be a day that you will not have any problems at all. We all went through those frustrations and had to learn the process that worked the best for us. For me pinning is my best friend.
Don't give up....keep at it and you will be amazed at what you can accomplish. Don't be too critical of your work because most people won't even notice anything but the overall beauty of your quilt.