You get the W2 for all your income and withholding for the whole year. It doesn't matter if you were part time or full time. If you did not have enough withholding taken out you need to give your employer a new W4 here to increase it. Nothing you can do about the past now. You might check with the employer to see if he used the right withholding table to look up the amount each paycheck.
And the IRS is always changing the withholding tables so you have less taken out each time instead of getting a big refund at the end of the year.
