Welcome to the QB from SE Michigan! Sewing a straight seam can take a bit of practice when you are new to sewing. The more table space the better. If you can use a dining room table or something like this you will be able to guide your fabrics a bit easier as you are sewing. Be patient with yourself as you are learning. I frequently find myself getting off my 1/4" quilting seam allowance if I am speeding to fast. Taking my time with my sewing always provides me the ability to get the seam allowance I need weather I am doing 1/4" for quilting or 5/8" for garment making. Give yourself time and you will get it. We have all been there. Again welcome to the QB.