As we can't see the tax return you filed using TurboTax, here's what you need to do to determine why the amount of your refund differs from what you submitted.
You should first do a line by line comparison between your Notice of Assessment (NOA) and the PDF file of the TurboTax return you filed. Your NOA may also tell you if there was a change made to what you filed. Often times there is an extra tax slip out there (T4 from a little job you missed, or T4E for EI benefits you thought were paid in the prior year), and CRA will add this to your tax return when they assess it.
If you are still unable to determine yourself where the difference lies, you should contact the CRA General Enquiries number and ask for an explanation. They can be reached at 1-800-959-8281.