Your download could have been corrupt. Try it again.
A video of the basic process is below. It assumes the end user is using CyanogenMod, but the process is identical for Coby tablets. Ignore the bit about the Play Store Fixer, as it has nothing to do with installing the Play Store in the first place.
Did I say you had to run through the entire rooting process again? No! I said that your Google apps download may have been corrupt. Download the 20120429 package and try installing it again through Clockworkmod.
If, after downloading the Google apps package again it still fails to install, you may have to manually install the apps by copying them to their right positions using a file manager.