You're making it hard on yourself. Stripped the failed attempt out and start over. With a little searching on YouTube you'll find videos to help you strip it out, there's no need in waiting for a response here.
The Chinese plastic tanks on Ebay/Amazon work fine. I think they ruin the looks of the trike though, and now you'll have that vent tube to stick up and look out of place instead of the clean look of the OE vented metal cap.
I've used Red Kote on cars, motorcycles, and ATVs and never had a problem. Some tanks I've lined I still have 10-15 years later without any issues. It's a quality product that takes patience and thoroughness to use. You could try practicing with some red food coloring in cooking oil to learn what you need to do to make certain you're moving the tank properly to coat everywhere and not allowing it to pool in the corners. It's easier to add more than drain out the excess. That's much less expensive than having to do it over.
The story of three wheels and a man...