I have the same issue as you do, rh71. My X is also white.
What I do is to ask some paint from BMW dealer (just a few ounce) and then use the brush pen (as small as possible) to apply at least 2 layers of the paint.

Then wait a few days for letting dry. Make sure the dried paint form a kind of "bump". Then rubbing the "bump" with soft cloth with a little amount of car polish until it is smooth. If you don't satisfy with the result, you can repeat the same procedure again.

Make sure you request the paint from BMW dealer, because from my experience, the paint is better than what I purchase in the shop and also avoid the tiny different in color.

Hope this can help you and Good Luck.