Hiya I'm Taz a girlie in my mid 30's I live near great beaches and love surfing well watching others

anyway, I injured my back (at work) about 10 years ago and struggled with putting on weight and generally moving around, having said that I've built up the muscles in my back, had physiotherapy and have been given the all clear to begin surfing, I had lessons before the injury and could stand up all e it briefly

before the injury. Both my lads surf well and I'm good at paddling my board a 7'4" Hobie mini mal which as loads of volume and suits me fine, I'm 5'4" and weigh around 12.5 -13 stone depending on the time of year

I'm still losing weight slowly and steadily.
my question/problem is I find that I'm frightened (of hurting my back) or just cant pop up is there anything I can do to helpl with this any exercises to aid the transition from belly to feet

or do some people just use their knee all the time

I can catch waves but have a psychological/physical block to popping up
I also have a 9'6" long board would it be better to practice n that?
any help would be brilliant
Taz