Stuck in the end

I was fighting the ender dragon and died. Upset from dying, I went into creative and used /setblock to set an ender portal, so I teleported to the end.

However, when I did that command, I was right next to my bed so when I beat the dragon and went back to the overworld, I spawned on top of the end_portal next to my bed and instantly get teleported back into the end. I'm on version 1.12.2 and I've tried the /execute command but it tells me entity 'in' cannot be found. What should I do?

Nether portals won't light with normal means while in the End, but that doesn't mean that they cease function completely.

Use /setblock ~ ~ ~ portal and you'll be spat out into the Nether through an auto-generated portal. Re-enter the same portal and it'll spit you into the Overworld.

You may want to consider breaking the end portal block once you've returned.