Thank you so much to all of you who posted such helpful comments and tips on my previous post! You Ladies are the best! :)
It seems like you all agree that the tightness of my socks' ankle was due to the fact that I didn't make the heel deep enough...

So, I ripped off my work until the Afterthought heel opening, I redid it but I didn't make the 8 decreases I had previously made...
I think I am going to put the cuff on hold for now because I am too impatient to work on the heel again and to follow your instructions to make it deeper... I need a little success now... ;D
Here are some Lilac flowers from my garden for you Ladies, to thank you for taking time to help me here and for caring about another knitter's distress!
[Click on photo to enlarge]
You made me feel better about that new sock experience and more confident about being successful with it! :)