Undoing 301 redirect?

One of my earlier sites was built on an expired domain and after working on it for a year it just wouldn't cross position 11.

So after researching I read that expired domains can be finicky and so I should 301 to a new domain.

Well I did that and it has been 2-3 weeks and it has disappeared. Now I am thinking I will undo the 301 and work on it again.

What do you suggest?

Yup, you can redirect again mate.

Yes you can do it.

Read More Here:
https://moz.com/learn/seo/redirection

https://moz.com/blog/accidental-seo-tests-how-301-redirects-are-likely-impacting-your-brand

I have reversed the 301, how long before it starts to pop back? I feel like I might have screwed it up big time.

301 is permanent so it is kind of hard to reverse that and get your original results. I would suggest looking into using Google's change of address tool: https://support.google.com/webmasters/answer/83106?hl=en