Yes, eventually you will get nasty letter from the IRS if you do not report all of your income on your tax return and they will let you pay a penalty and some interest on the income you failed to report.
Every W-2 that you received must be reported on your tax return, even if they are for small amounts. Remember that each one of those W-2’s has your Social Security number on it, and that income was reported to the IRS by the employer. You do not want to get in trouble with the IRS for under-reporting your income.
ALL of your W-2’s must be entered on the SAME tax return. After you enter the first one, you click Add Another W-2.