Don't worry about the time, you will get faster as you do more sewing - at first it is better to aim for accuracy rather than speed.

Are you pinning the fold?

I should have mentioned that, but I have been sewing for so long it can be difficult to remember that for some people it is all strange and new.

To match up the seam line place a pin through the same point in the pattern each side, such as where a red and yellow stripe meet. By putting the pin through both layers of material you can see that if the pin is perpendicular to the fabric the two layers are exactly matched. Hold the fold carefully, take another pin and slide it through layers so they are hold together and the pin is still perpendicular. You can now remove the first pin. If you put in pins at each horisontal line at first it should help keep the lines matched up.

I think that you made the right choice of stripe, it is going to look really smart.