You might want to replace "I only have one" with "My only..."

My only distinct memory from the movie is Bingley's proposal to Elizabeth.

Otherwise, a semicolon is a good option:

I only have one distinct memory from the movie: a scene where...

You might want to replace "I only have one" with "My only..."

My only distinct memory from the movie is Bingley's proposal to Elizabeth.

Otherwise, a colon is a good option:

I only have one distinct memory from the movie: a scene where...