I just failed training with one of the regionals and busted my checkride. They asked me to resign which I did instead of getting fired. Now I’m wondering is my airline career over or do I still have hope ?

Apply at Mesa.

Lol...I'm not sure if that is intended to be a joke or if you were being serious. Retreads is the industry term I've heard thrown around.

I got off the phone with them and they said they’ll call back today to let me know if they’re interested. Should I be worried?

Only if they say yes. Then you’ll be working for Mesa.

I kid, I kid...

Hope they take you and you redeem yourself and have a long and successful career.

Don't be in a big rush to cold-call other regionals just. You need to figure out what went wrong, how you can fix that, and equally importantly, how you can articulate to a potential employer that it was learning experience and not a sign of fundamental unsuitability.

I would probably try to some other regionals once you've figured out your way ahead with mesa and go-jet as last resorts.

Worst case maybe you'll need to go get some 135 time and apply to regionals again in your two (with some turbine training sucess under your belt).

Atlas....Atlas/Southern is a last resort. You could probably start training tomorrow there.

I have 0 jet time

How old are you and what are your times?
Are you early 20’s and just woke up with your head up your @ss come checkride day or are you late 50’s and you just can’t learn new sh!t anymore?
I’ve known both.

I’m early 20’s. 1500 hours, also failed my checkride because of a visual approach, never practiced visuals in the sim before. First time doing a visual in a jet was on my checkride