I hope you have a good quality balancer that you bought from the hobby store - they make things a lot faster and simpler. All props should be balanced by the user and trying to return them will probably get you laughed out of the store, because most fliers never balance their props. Here's how to do it:
If you need to remove weight from a heavy tip, DO NOT shorten that tip. Lightly sand the backside of that blade to remove some weight, never the frontside of the prop, nor the leading or trailing edges. The farther out toward the tip you remove (or add) weight, the better, as a little at the tip equals a lot more, farther inboard. Sand a little, check the balance, sand a little more. I never use anything more coarse than 120 grit, usually using 240 grit.
You can also add weight to the lighter blade by LIGHTLY spraying it with some paint. Again, spray the backside of the blade. Many people like to use a clear spray paint, but I like to use a color so I can easily see which prop I have balanced. Give the paint a couple of minutes to properly dry after each spraying, as any remaining solvent in the paint will give you a false reading. And take it easy, a little goes a long way.

btw, they don't need to be "perfect", just well balanced.