Should i enter a w2 from 2018 that i couldnt find at the time or dont even worry about it ?

If you filed a 2018 tax return and did not include ALL of your income then you must amend that tax return to include it.  It was reported to the IRS by your employer--the IRS expects you to report all of your income.

https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend

https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed?jump_to=answer_3288565

A 1040X cannot be e-filed.  It must be printed and mailed.  It will take about 4 months for the IRS to process an amended return.  It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.

Wait about 3 weeks from mailing and you can check the status of your amended return:

https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1

https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-questions

You should amend your 2018 return to include the wayward W-2.  You will be contacted at some point by the IRS and it's better that you deal with it now to avoid tax penalties.

Please see the instructions contained in this TurboTax Help article to amend your return:   How to amend (change or correct) a return you already filed