Well I can't really tell what the problem is with this detail. You either have to post a video or specifically explain. But some things you can try:
- Make your stance fully side-on so there is less of your body the bowler can target
- Get deeper in your crease to give yourself more time
- Keep your head still as possible when the ball is being delivered
- Pick up length from the bowler's hand and not off the pitch. This is crucial if you want to give yourself more time, it takes practice
- If you're being beat by yorkers/full length deliveries, lower your backlift
- If you're being beat by bouncers/short length, raise your backlift
- Stop being a sissy and take a few hits. You can pad up your whole body if you're that scared, start lifting weights to your body stronger
The only way you're going to learn to play fast bowling is by constantly practicing against fast bowling. Man up.