Aside from everything that others have mentioned, I have to ask if you are using a physical barrier while sewing your seams? I find that using a barrier helps me sew seams much more uniformly compared to when I was just eyeing it based on a marking on the machine bed, and way better than when I was trying to eyeball it with a quarter-inch foot. There are other types of physical barriers, such as this one:
https://www.amazon.com/Guidelines4qu...dp/B005NGX8M8/
Some people use a stack of post-it-notes. I like molefoam because it is less expensive and I can make it as long as I want. Here is a link to it on Amazon:
https://www.amazon.com/Dr-Scholls-Mo...dp/B0009MI9CA/