Withdrawals are not the best of things, but aren't all that big a deal if you only have a few. If you are re-taking a class after getting a low grade, keep in mind that AMCAS includes *all* grades in their GPA calculations, regardless of your school's policy.
<rant>My school's policy was to not include the lower grade in GPA calculations, and therefor re-taking a course was thought of as no big deal, to the point that they often wouldn't allow withdrawals because of this "easy" solution. They also didn't allow incompletes to stand, so anyone who was in a situation where they COULD NOT make up a course (like the prof left the school before the following semester started, as in my situation 😡 ) was given given an 'F', given a pat on the head, and told it was no big deal, just re-take it later. Because AMCAS follows their own set of rules, they take away the autonomy of the undergraduate institution in determining GPA. Result? Theoretically, you could graduate summa cum laude and have AMCAS report your GPA as 3.3. AMCAS says my GPA is 0.15 lower overall than it actually is, all because of 1 class.
This policy of AMCAS is, IMO, just plain WRONG. But I don't know what can be done about it. Not like it kept me out of med school- I got in- but it seems like something that should have a legal challenge coming in the (hopefully) not-so-distant future.</rant>