Adv F as a whole is so pretty and I love the music, especially for the port de bras.
I'm just so happy I've found an adult ballet teacher who's so dedicated to letting us learn the trickier stuff - we may not always be exam standard but testing our limits as dancers makes other things we were struggling with seem like a piece of cake in comparison. I'm glad to see others on this thread have equally passionate teachers.
As for glissades under/over, I still remember the old Grade 5 exercise (Glissade stretch bend, glissade stretch bend, and under and over, changement, stretch bend) which helps me keep straight which leg is going where. Whether you're going under or over you swap which leg you had in front. Overs always made more sense to me - you go towards your back leg and bring it in front. Unders you take your front leg to the back.