I also have to give myself props on the color selection. Somehow I managed to match the red in the car seat almost exactly, which I love. Just a couple of things about this tutorial:
1) To give yourself an easier time with the seams, etc. I suggest using 1/2 inch seam allowances rather than the 1/4 inch suggested.
2) Remember that most of the measurements in the tutorial are for the FINISHED project, so in order to have seam allowances as stated you have to add that length to each cut piece of fabric.
3) On the straps: I just made them about 8" long AFTER they were sewn and both ends closed. This meant that in order to place them correctly on the car seat cover, you just fold each in half, mark the halfway point with a crease or fabric pencil, and then sew it in 2 places: 1/2" to either side of the middle crease.
4) Also, when placing the straps, I think that were I to make this one again I would place them closer to the center. They are placed 11 1/2" from the outer edges (sides, not top & bottom) of the cover. I personally would put them closer to 13" in. They slip just slightly down the sides of the car seat handle when sewn 11 1/2" in, and I think just a little closer to center would be better.
5) The directions for placing the straps are a little vague: I marked the distance in and down on the main body of the car seat cover, then placed the straps by finding the exact middle of the strap and matching that point to my mark, then sewing on my pre-drawn lines.
6) If you are piecing the main body of the cover (like I did and as shown in the tutorial) I made the bottom accent (the red) a total of 4" tall. I personally like that amount, but I wanted to give anyone making this an idea of how big that panel is. So, the red on the bottom is 4" and the patterned piece is 38" for a total of 42" in height.
7) The curved corners are a matter of eyeballing it. I think I made mine so that at the deepest point (aka, the point of the square corner to the center of the curve) about 3", and it worked well. I might consider doing about 4" next time to avoid the corners dragging on the ground, but it's pretty even.
I had to include a picture of the cover flipped up, if only because I'm so proud of that color match (OK, almost match, but still). I also love the monkey strap pads that my mom got us. Granted, our car seat came with cushions on the straps already, but these were too darn cute not to use!!!!