Hola, voy a explecarte en Ingles por que lo entiendes mejor. It basically means you are hurrying/rushing to do something too fast. You are not taking a matter/situation or task one step at the time. Example: "This is great, I am going to do a PHD after I do my Master degree!" "You are getting ahead of yourself my friend. First complete your Bachelors degree" That type of thing...

Sometimes in conversation we tell people the end of the story before they have all the facts. This confuses people. We may then tell them "I am getting ahead of myself" and start the story over, so they hear everything in the proper order.

" I'm getting ahead of myself " = I am doing things too quickly/ I am jumping to conclusions