That's really looking the biz Aaron, very nicely done. Take it steady doing the white stripe and you should be fine. Might even be easier to it with a brush, as it only needs 'bringing into line'. Paint out the stripe where it infringes into the red, let this harden fully, then mask lightly, using low tack tape such as Tamiya, and 'straighten' the line with white paint. Once fully dry, clear coat should make it look the same as the surroundings, and it should blend in nicely.