"This is my fault."
Translation:Esto es mi culpa.
Esto is the neuter form, so it is used for things like "situations" of undefined gender. The masculine form is este.
Esto, eso, and aquello are the neuter forms, and they are handy. "Eso es ......" is a good way of saying "that is ....." when looking at a lanscape, crowd of people, street scene, etc.