Hi
School PE is shit. It puts dyspraxic or plump or unco-ordinated people off being physically fit, sometimes for life. It simply doesn't meet our needs. I was like you but I adore exercise now.
My advice is: start small. Find some 10 minute classes on line. The easiest ones are probably 'Walking with Lesley Sansome'
You can do the same with bodyweight classes online - 10 minutes of simple exercises - Marching and high knees etc. Again, go for beginner levels and look for instructors who have a student behind them who does modified moves. You could try Rosemary Conley. Old school but easy to follow and all fitness is fitness.
If you want some stretching, try yoga. Adriene is good and so is Kassandra. Watch a video a couple of times while you have a cup of tea, so you can see what they do next and what each move is called, (otherwise you'll feel all confused and give up) then have a go. Opt for their beginner classes.
Mix them up. Do 10 mins walking with Lesley one day, then 10 minutes bodyweight (that's classes that use your own weight to make you stronger, no equipment needed) or yoga next day.
Do 10 mins every day, at a convenient time - first thing or after DC are in bed or before your shower etc. Then once that feels too easy, add another 10 mins at the other end of the day or explore 15 or 20 minute classes and build up to full hours. There are thousands of good free classes online
Set mini daily challenges: walk to the shops for food. Carry heavy shopping bags home and think of it as an upper arm and shoulder workout. Walk to the next bus stop on your commute. Take the stairs/walk up the escalator. Go for a brisk walk at lunchtime. Do 10 squats while you clean your teeth or 20 high knees while the kettle boils.
If you have children, (of any age, including adults) build active time in with them - go for a hike to catch up with them, try kayaking or go for a swim or hire bikes. Play with beachballs that are light and slow so us uncoordinated people can actually catch them! Join them for a bounce on the trampoline. Go on dog walks with friends.
Honestly, I would do this stuff for at least three months before venturing out to join a class or gym. You will feel so much more confident if you've done a but of prep at home first.