I think maybe you are being a bit hard on yourself and that your work is well within acceptable standards. You might not win a quilt show prize, but if that is not your goal I think you are ok. We have such high goals for ourselves, but fabric can be treacherous! If the goal is to match the stripes better (not saying you have to) that's more cutting than sewing and will be tough to match.
For me, I am the most accurate when I use pins, when I press my seams open. My fabric is pressed a lot, every step, I don't use starch myself. I spent my first couple of decades being very precise with my cutting and stitching. For the last couple of decades I also tend to cut/sew large and trim down -- I get better overall results, I really waste very little fabric, and it is more fun and faster for me..
I think your desired pattern will be great -- have you considered instead of making geese units, just putting together two HST (half square triangles) -- does that work better for you? I think the scrappy design will make any close up imperfections fade quickly.
Final thoughts -- I believe in repetition and that piecing is at least as physical an activity as playing the piano. At least for me, it takes constant practice to keep my sewing skills up. We start out a bit rusty and we get better. Sometimes I designate some things as practice and just sew up a bunch of 9-patches or whatever to warm up before a major project. While fabric is treacherous, some times we are adding in our own tensions and pulling or pushing instead of letting the machine and the fabric do the work for us. Deep breaths and sally forth!