Issues with Brake Lines

Hi all,
I am looking for some help in regards to some issues I'm having with my brake lines that I recently replaced on my 2012 Veloster.

For some background I had a leak in my brake line about midway down the line to the back brakes, I decided to replace both lines as they were very rusted and did it myself over 2 days. after replacing the brake lines I filled the master cylinder reservoir and bled the air out of all the calipers going RR, LR, FR, FL using the 3 pumps and hold method. The brake pedal afterwards was still soft and would go to the floor/couldn't build up pressure. I am pretty sure the master cylinder reservoir emptied completely while I was replacing the lines so I bled out the air in the master cylinder and re-bled all the calipers in the same order as above. This didn't seem to fix the issue as the pedal was the same as before. I also have checked all the connection that I installed for leaks and that doesn't seem to be the culprit.

My thoughts are to either replace the master cylinder or bleed the lines with a vacuum bleeder instead but I would love any advice for things I could have done wrong/missed.

Thanks for the help and if you have any question I will try to respond quickly.