I can land small drops by doing manuals but if the drop is more than 3 feet my feet get off the pedals (same during the jumps) what should I do, what is the correct technique?
Make sure that you aren't jumping or pushing off of your pedals; you should be scooping them up with you. I'd suggest that you try to practice lifting your rear wheel off of the ground without using your front break. You do this by pointing your toes downward and scooping upwards with your feet while shifting your weight forward. If you can manage to figure this out you should be able to use a similar technique to keep your feet in contact with the pedals while in the air, although you won't usually need to pull up on them as hard.
It is tough to help, as I don't know what exactly is going on but I would start there and see if it helps
Make sure that you aren't jumping or pushing off of your pedals; you should be scooping them up with you. I'd suggest that you try to practice lifting your rear wheel off of the ground without using your front break. You do this by pointing your toes downward and scooping upwards with your feet while shifting your weight forward. If you can manage to figure this out you should be able to use a similar technique to keep your feet in contact with the pedals while in the air, although you won't usually need to pull up on them as hard.
It is tough to help, as I don't know what exactly is going on but I would start there and see if it helps