I admit the curves are a bit tricky, but there not hard to do. I think I was only able to do it because I have sewn for a lot of years.
All I can say is follow your lines, sew very slowly. It would be much easier if you could watch someone do them.
But you can do it...........what I would suggest, pin at each end to start with, put a pin in the centre and then try. Once you have done it the first time there will be no stopping you. One other thing sew from the inside, don't try to sew from the outside............clear as mud I expect!
Lets know how you go anyway. :D