The oil guage will never let you know about oil volume, it only measures oil PRESSURE which is a totally different integer...don't feel bad, MANY people have drawn the same conclusion.
But...the oil has got to be going somewhere. I don't know your location, so I am limited on options to give you. With so little milage, I'd try and bring it to a shop where they can hook it up to a computer...it can't hurt. Several places will do it for free...hoping to get your business for the repairs. Depending on where you live, that may not be the correct oil for you...just depends.
Also, did you check out the oil level immediately after having it changed? If for some reason, it wasn't full to start with, it wouldn't be full later on either. Some people (most shops) drain out the old oil, put in a pre-specified amount, and then never check the level on the dipstick.
Check it out and get back with us.
I'll try to help you however I can.