I would suggest you have a stop loss in place on your SHORT position, as MAGS will be much higher in the coming weeks. I say this as your post appears to be written with FUD (fear, uncertainty, and doubt).
As for trading on margin, that's a very personal decision. What is important is how you manage your money, not whether or not you trade on margin. If you can manage your finances and trade on heavy margin, and you're adept at trading, margin should not be an issue.