Trouble merging 2 cloud points

Merged files are mirroring each other, this part is about 3 mm thick, scanned front and back

You need to use manual point alignment if this error occurs, the software can’t see the sides well if there are not specific unique features for each side .

If you object don’t have any features , scan using RGB color in marker mode and paint your reference markers or stick a sticker for reference on top of the model then use manual mode for merging . The sticker going to be your reference point

The only thing missing from your reply was the sticker, I did everything as you describe.
I will try the sticker trick later on.

I purchased on Amazon little white dots stickers for use in situations like that , it allows me to place precise the marker point later while merging , but it can be even a painter tape just small fragments for a reference . If you scan in color it really don’t matters , a color pen marker will works too.