It sounds like your pretty sensitive to the effect, but everybody who smokes dope eventually gets concentration and memory problems. Sometimes it needs testing to show the difference, but mostly other people notice even if the user doesn't. How bad it gets depends on things like how often you smoke, how sensitive you are to the effects, what else in in your system at the time (alcohol, heroin, medications, speed etc.), your physical condition and your state of mind.

The same sorts of things can effect how long it takes for you to recover, and daily smokers take longer to recover than an occassional user. Being stressed or using other substances prolongs the effect, and so can regular cigarette smoking. But, in your case, you will probably be pretty much back to normal by the time you read this. For someone who has only been using for a short while and has not become dependent on marijuana, your body should be free of the active ingredients in about a week and your short term memory should be OK again then, although you are not going to get back the memories you "lost".