After the complete disaster (on June, 18th), I unstitched all the different pieces, I washed them so that one cannot see that the fabric had already been stitched, I ironed again all the parts and I started thinking about how to assemble the capri pant.
I finally opted for a different approach: assemble the front and back of each leg and then assemble the two legs together.
Here we go!
I couldn't manage stitching the two legs together in just one go. But I am pretty satisfied with the result.
Thanks again to Astrid for her easy and ideal for beginners patterns (Les intemporels pour Enfants - in French).