I did the full erase on my old iPad and want to trade it in, but I forgot to turn off "Find My" on the iPad before I erased everything. Is the Activation Lock still on? Do I need to do anything else before sending in to Apple?

To quote from the provided link… proceed from (2).

If you no longer have your iPhone, iPad or iPod touch

If the steps above weren’t completed and you no longer have your device, follow these steps:

1. Ask the new owner to erase all content and settings using the above steps.
2. If you're using iCloud and Find My [device] on the device, sign in to iCloud.com/find or the Find My app on another device, select the device, and click Erase. After the device has been erased, click Remove from Account.
3. If you can’t follow either of the above steps, change your Apple ID password. This won’t remove personal information that’s stored on your old device, but it will prevent the new owner from deleting your information from iCloud.
4. If you’re switching to a non-Apple phone, deregister iMessage. 
5. If you're using Apple Pay, you can remove your credit or debit cards on iCloud.com. Choose Account Settings to see which devices are using Apple Pay, then click the device. Next to Apple Pay, click Remove.
6. Remove your old device from your list of trusted devices.

See >>> What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support