Why is my SEP contribution calculating for employer not employee? I am a sole proprietor and am the only employee.

A SEP is an employer-only contribution retirement plan.

If you want to make an 'employee' elective deferral, you would need to use a different type of retirement account, such as a 401k (and it is too late to do that for 2018).

you, as the owner, must use the employer rule.

a sole proprietor can never be an employee of that business