Did you tighten all the bolts with the suspension compressed? Was the front jacked up evenly or one side at a time? Has the car been aligned?
A quick thing that may or may not help is to leave the car on the ground and if you have a stock strut bar, loosen the bolts for it on both sides, then tighten them again. That kind of thing can give twitchy steering, especially if one side of the car was jacked up at a time.