Hey there, @djagiella.
I'm here to help you get up and running with your new QuickBooks 2018 edition. I have some steps I'd like you to take to verify everything is set up properly with your terms. Even though you have the 90-day term set, it could be the term itself is not set properly for 90 days, or you might need to Rebuild your data. First I'll have you verify the term. Here's how:
Pull up an invoice once more. If you're still seeing the past due stamp, I recommend Rebuilding your data. Here's how:
Note: it is highly recommended you perform these steps on the computer hosting the company file.
Once the Rebuild is finished, try creating a new invoice to see if the issue is still persisting. If it is, I've attached a helpful article with additional steps to troubleshoot data damage in your file. You can find that here: https://community.intuit.com/articles/1501314-resolve-data-damage-on-your-company-file .
Should you want to work with an agent directly, I've also included a link to the Contact Us page: https://help.quickbooks.intuit.com/en_US/contact . If you have any questions for me, leave a comment below so I can get back to you.