Updated: Jul 21, 2020
A sketch is like a drawing of a scene. It describes the scene and what can be seen.
To make a story there has to be a character(s) and the character(s) have to change in some way during the piece. The change can be tiny but it must be there. It could be coming to terms with a loss, understanding something better, doing something, whatever but it must be there.
In the short story ‘Araby’ for example by James Joyce, the character is changed, perhaps by being thrust into adulthood before his time?