I need to know what can happan if you dont close a “magic circle”.

What would happen if you do not close a magic circle? Well, I would have to say that would greatly depend on what the magic circle that you did not properly close was being used for. So, to actually give you a more specific answer in this case, I would need to have a few more details as to the type of spell or ritual that you were performing before I could really say what the effect would be with any level of accuracy. In some cases though, it could be something as simple as the spell or ritual not working. So, in that case, it generally is not any real big deal or problem. You are out a little bit of time and whatever expendable items you were using in that preparation of the magic. But as to lasting effects or any unforeseen maladies or ill happenings – well, I would think that you would be quite alright in that case. But, of course, if the initial spell was less benign, then the effects and repercussions of not properly casting the spell or ritual would no doubt be a bit less benign as well – just as one would likely assume. But well, if one were to be making use of such magic in the first place, them perhaps such an oversight would be considered something like karma anyway.