Keyframe Position is Not Retained to the Next Keyframes

Hi all,

Would like to seek help on below.
I’m trying to follow lecture 16 of “The Ultimate Blender Low Poly Course 2” but I’m not able to position the object in such a way that it will retain its form down the next keyframes.

Before I have started positioning the object, I have blocked first the direction where I want it to go.
Then after that, I started position its parts.

This is the position I want my object to retain in the next keyframes. This is on 155 keyframe:

The goal was that the object should dive from the platform to the water but whenever I try to go to the next keyframe it does not retain the form I have done. Below image is only on the next keyframe (156)

This is my file:
Lecture 16 - Animating the Human part 2.blend (3.6 MB)

Thank you in advance.