Worry not my friend... The bracing idea is fine, if necessary just cut into your existing lines with some black paint to clean them up. A steady hand doesn't come overnight Sometimes I will use my pinky as a maul stick (an old sign-painters tool)
http://en.wikipedia.org/wiki/Maulstick
We are always the most critical of our own work...I think you're doing just fine. Do some practice on a some paper with strokes just to get an understanding of the brush down. But like I said if you cut into that with some black paint you can straighten that up easily. Good Luck!!
PS: I have been mentored by a sign-painter for the past 10 years so I came into this hobby with a little more knowledge then most about brush technique, but this is so much smaller scale and takes time, but remember anything can be fixed or altered, nothing is lost. It's just another step in the creative process.