I'm afraid I won't be much use in that regard—my magic's awful at small things as well.

[ says the person who can't do subtle in the slightest ]

If the problem is the magic just 'happening', perhaps you simply need to use it more? Or push yourself harder when you're actually using your magic to try and tire yourself out so these accidents don't happen. Of course, this is all pure speculation. English magic doesn't have these sorts of problems.