You will report the actual income you received on your return. If the 1099-Misc you received from the client is less than the correct amount, you would enter the amount reported on the 1099-Misc and the additional amount would be reported on Schedule C, line 1 "other gross receipts or sales not reported on a 1099-Misc".
However, if you received a 1099-Misc from a client that overstates the amount they paid you, then you should contact the client and request a corrected form before filing your return.
