I just couldn't get that 1/4" seam either, no matter what I did, and even with a 1/4" foot. I finally cut some test material, put it front side down on some fine sandpaper (so it wouldn't move or stretch) and drew 1/4" seams on my material. A lot of material, by the way. Then I started sewing, carefully keeping the needle centered right on that 1/4" line I'd drawn. You know, it really didn't take me all that long to figure out what I was doing wrong. I measured and measured. As long as I stitched on my line, I was getting perfect 1/4" seams. Which served to prove that I was reading the 1/4" foot all wrong. By continuing this process, I learned to "read" the foot correctly. It was a small error, but a huge one when magnified over and over. I now, finally, sew 1/4" seams. Now I'm working on that ever elusive "scant" 1/4" seam, whatever that is. I know if I'm going to do this one, it has to be consistent. But lots of patterns call for it, so I'm going to learn it, whatever it is.
Just keep practicing. And take that tutorial! You'll get it.