Are you sure the problem us even in your sewing? It could be in your cutting, pressing, even thread choice...But I will say that I've had the easiest time getting a consistent, perfect 1/4" on my narrower (4mm and 5.5mm) stitch width Berninas with the #37 and #57 feet. They're the same except the #57 has a sturdy metal guide to the right. I also love a screw-down seam guide, which is a very inexpensive item. Just know that on some machines, one thing or another prevents you from getting that guide that close. The only answer is to experiment. I like to make a block using strips cut at 1.5" like a 6-strip rail fence (12" finished block) or a double nine patch (9" finished block) or a goose in the pond, when I think I've got the 1/4" worked out on a new machine. A simple block with several seams across the width will show you if you're really being accurate. A quick test is to sew three 1.5" strips together, press, and measure the center strip, which should be exactly 1" across. But do a block with 11 seams across the width, such as a 6 strip rail fence, and you'll definitely find out if you are off!