We cannot see your tax return so we cannot know for sure what is happening with the calculations, But when you added a W-2----you added taxable income. More income = more tax. That extra income might be eating up some of your recovery rebate credit, which can be used to pay tax you owe.
if you filed for the Rebate Credit,
when you amend you must continue to file for the Rebate Credit.
if your new W-2 pushes you over the AGI limit, you may no longer be eligible for the stimulus checks.
Don't file until you get the original refund.
Look at the form 1040X …
Column A should have the figures from the original return, Column C the corrected figures and Column B the differences between the other 2 which needs an explanation on page 2 of the form 1040X.
If you completed it correctly you will see an entry on either line 16 OR 18:
On line 16 should be the amount you paid with your original return. If you paid nothing already then this line should be zero.
On line 18 should be the amount of your original refund you received. If you have not received your refund yet then you need to wait for it. If the refund changes from what you expected then this line must reflect that change.
Then you will see your extra refund on line 22 OR the new balance due you need to pay on line 20.