we need numbers to answer you. how often is often? and how much is a little bit? because the main nutrient floor for women is 1200 cals. which means that unless you were specifically planning it out [most likely with the help of a registered dietitian], it's very unlikely that you're getting all the nutrients you need in fewer calories. your specific 1300 bottom range number means that you are closer to your goal or a lot more active than most people. which isn't a bad thing, but a previous poster is right in that when you maintain your weight, you'll likely be doing so at a much higher range, so figuring out how to get into your loss range is just the first step.
so back to the original questions. if you're within about 50 cals, maybe up to 100 or so that's less of a problem. as far as often goes, if this is less frequently than every other week, i'd say not to sweat it. but the higher the amount your calories are off by or the more frequently your off the more you need to address this issue.
one other thing that you can do is to average your calories on a weekly basis. in other words, does that off blip mess with where you are, on average, overall? as long as you are [and you aren't eating 2400 cals one day to make up for a 200 cal day or other extreme things like that] about where you should be a little bit off here and there isn't a big deal. it's just you do have to pay attention to when a little bit off becomes a lot off and every now and then becomes a few times a week that you get into trouble.
-google first. ask questions later.