I don't understand how Meena's group was created since her group made the scratch but was Karkat the one who made the ecto clones... and I don't remember if Karkat's group made a scratch so the portals would change places

Karkat did ectobiology and the meteors that sent Meenah’s group back were glitched so they were sent to a session that they hadn’t been spawned in. This glitch is the reason Meenah’s group had to scratch the session.