I personally have and do use both spellings without apology, but........
From what I understand the difference is more or less.........
Magick is: "Ritual magick used by Wiccans and Druids and such like folk in the performance of Magickal workings and spellcasting."
Magic is: "Performance magic usually seen on a stage for entertainment. Card tricks, slight of hand and sawing a lady in half."
I am sure that is not the only difference people know about and I hope someone will come and give another.

But I hope this helps a little Katie.

I am going to leave it here for now, but when it is quieter and the post has been answered as fully as you require I may move it to the Wiccan Wanderers section, if that's alright with you.
Lady C.