Yes, you can be charged with it if there is "reasonable cause" to believe it was yours--and if drugs are taped under your car, or under a car you were using or were in (and under "your side"), there may be "reasonable cause" to think it may have been yours. That does not necessarily mean you will ultimately be convicted: to be convicted, the proof must be "beyond a reasonable doubt," which is a much tougher standard; there are things that could provide reasonable doubt, such as if this was not actually your car (you don't say for certain in the question), so the bag could easily have belonged to the owner--that could right there create reasonable doubt. However, the standard for an initial arrest is lower than the standard to convict, and if the drugs were found "under [your] side of the car," that could be enough to provide reasonable cause to arrest or charge you.