I dragged photos onto a usb stick and now all those photos duplicated on photos

That is expected to happen, when you drag photos from a stick into an album in Photos. The photos will be imported. usually Photos will not import duplicates of a photo, but that applies only to exact duplicates - if you import the identical file again.

But when you drag photos from the Photos window onto a folder on your stick or Desktop, you are exporting the current previews of your photos, not necessarily the original image files. SO you created new image files on your stick and when you drag them back into your open Photos window they cannot be recognised as already imported and are imported again.

You should find all duplicates together in the "Imports" album in the sidebar. You could simply delete this last import by selecting all photos from this import session together in "Imports".

Hey there mopeede,

Thanks for reaching out to Apple Support Communities. We understand you’re seeing duplicate photos after moving them to a USB storage device. We’ll be happy to help with this.

If you delete one of the photos in question, do both copies get removed? If so, try repairing your Photos Library with the steps from this link as this can often resolve issues like the one you’re describing:

How to use the Photos Repair Library on your Mac

We hope this helps. Take care. 

The original file is stored in the library - dragging from photos is just a way of exporting a copy.

If you want control of size and quality (you should) then select the images in photos, and use file>export instead. (Again this exports a copy - the original still remains in the library)