You know that envelope (invitation, response card, etc.) you just ruined? Don’t throw it out. Use it as a template to make your corrections. You now know where you don’t want your text. Make your corrections and just run it through the printer a second (or even 3rd or 4th) time. Just use a different color print each time so you know to where you’ve moved your text.
In the examples below, I’ve blurred the names and address. So don’t worry, your vision hasn’t gone selectively blurry.
When printing invitations, response cards, etc. ALWAYS ALWAYS ALWAYS over estimate how many you need and buy an extra box. It’s always best to have too many than to run short. You will ruin at least 1 when printing. If you have an unopened box you can return it (just stick the receipt in the box so you don’t loose it) or sell it (online, at a yard sales, give it to a friend, etc).