Having a different last name should not be a problem if you do the following:
On your tax return, enter in Personal Info the last name that the Social Security Administration (SSA) currently has in their database. This is because before the IRS accepts or rejects your return, the IRS compares your name and social security number to the entries in the SSA database.
However, when entering your W-2, use the name that is actually printed on your W-2 (in fact, enter everything on the W-2 exactly as printed). So long as your social security number is correct, this will not be a problem - you will not be the first person to have had a name change in mid-year.
If you need to update your name to the SSA, be sure you wait until after you get your refund, so that there is no chance of the IRS checking the SSA database and getting the wrong name.