Have you shield dropped the bomb immediately after pulling it out? It should be a little bit to the right of you. Also, are you falling into the water from the left of the bridge?
I always shield drop the bomb immediately. This is what happened the last ten times:
1. megaflip, miss the post, land where cow used to be
2. megaflip, land on the post successfully
3-5. explosion hits Link when trying to megaflip, fall in water
6. megaflip, land on the post
7. megaflip, miss the post, land where cow used to be
8-10. explosion hits link, fall in water