You should always wait for all of your W-2s to file your return. The IRS requires you to report all income on your return.
Employers have until January 31 to mail out W-2s, which means your W-2 should arrive any day now.
If you’ve filed your return already, you will received your stimulus as part of the tax refund based on that return, but you’ll need to file an amended return to report your additional income.
Yes you were supposed to wait for your W-2's so that they could also be entered on your 2020 tax return. You can only file ONE tax return. The IRS is not accepting or rejecting 2020 returns until February 12, so your e-file is just sitting on a server in pending now, and you cannot change it. Wait to see if it is rejected or accepted. If it is rejected then you can add the W-2's and re-file. If they accept it, then you have to wait and file an amended return later to submit the W-2's.