If you really don't like it, there are loads of ways of getting rid of it. While it is still fresh you can remove it with a colour remover such as colour B4 or Jo Bazz. (Assuming you used a dye that contained peroxide/developer.) These are not peroxide based, and don't damage your hair. Chances are you would only have to use it once to get back to blonde. It will be brassier than it was, but you can then tone it.
If you want to stick with brown but a lighter shade, vitamin C is the best thing for fading colour, this also works well on direct dyes (AKA semis, dyes that you don't mix with developer.) Mix vitamin C powder with shampoo (Head and Shoulders or a clarifying shampoo ideally) apply to dry hair, cover with a shower cap or plastic bag, and apply heat from a hair dryer. Wait at least 45 minutes then rinse with hot water. Smother in conditioner, cover again, add heat and leave for 30 minutes minimum. After rinsing your hair should be a lot lighter, without compromising the condition. You can use vitamin C masks several times a week.
If all else fails you can do a bleach bath, much less damaging than actually bleaching, but I would try the above methods first.