In my business we call this is an irrational fear..It means it not based on the facts, the statistics, but is none the less very real. Try to tell someone with a real phobia about flying to just relax on the airplane!!
So, two things
1. skip the beach, do not do this to yourself as going to the beach is not a necessity of life.
2. Go the beach and keep saying to yourself over and over...
Peter Benchly loves beaches, he just made a movie is all.
I have a 100 times greater chance of being struck by lightening, hit by a bus, or winning the lottery than being bitten by a shark.
If you are also deathly afraid of lightening or being hit by a bus, I would suggest taking Disney Grandma's advice and going to the beach at The Beach Club or Grand Floridian or Poly...
Peace....Ted