I used to think - up down up down when I was learning. It helped me remember what I was supposed to be doing. I also found it helps just to zone into the beat and not over-think what you are doing.
Your legs will prob hurt after your lesson and maybe your core. Most newbies use their legs to grip and not their core to balance. Try doing some core strengthening exercises at home to help your strength. Things I found useful were -sit ups, planks, thread the needle and also swapping your chair for one of those large exercise balls when at home watching the tv or on the computer. :)
It will take a few weeks for you to get the hang of it, try not to get too disheartened. Just remember, we all went through it