I have started trying to do a little self casting using candles. However, I did not end/close the spell. How important is it to do this and what is the preferred method? Thanks in advance.
Closing a spell depends on what practice you are using to do your spell. Typically in hoodoo, Santeria, or voodoo you simply thank the spirits or finish what your doing and leave it be. In Wicca and pagan systems I have seen people open up a circle (energy) and close it once they are done sort of like opening up a portal for lack of a better term. If dealing with an entity I normally bid it farewell and tell it to go forth and bring my spell to fruition.
Basically, it's as important as you make it out to be. The single most important component of any casting is faith. You need rock solid conviction that what you are doing in that moment will have tangible effects on the world around you. Anything that erodes that faith makes your spell weaker.
The fact that you made this post suggests that in your specific situation it could be an issue for you because you worried enough about it to consult people on the internet.
From a purely objective point of view, it doesn't matter. I personally like blowing out candles and burning things to add definitive punctuation to the end of my spells to set them in motion, but there's also a case to be made for letting the candles burn down on their own letting the energy of the spells slowly sleep into the world. Neither one is better than the other. It basically comes down to what your instinct tells you is stronger, and what decision will give you the most confidence that your intention will be made manifest.