One feature to take advantage of, if you aren't already doing it, is the "sandbox".  

 

You can create a "sandbox" of your account which is a clone of your current data, but any changes you make will be discarded when you are done testing.  So create a sandbox, import the games, fix errors, try again, see how the games look, play with the data until you get it to look right.  Then exit the sandbox and go do it for real.

 

Sandbox setup is in Other --> Site Archives.  Click the green cross on the bottom of the page to create one, then click "View" to activate it.