Return spring looks good...I think there is really only one way to get it in there...I'd still be suspicious of the soft part of the slave line...if you used an old one, they are definitely known to fail and not just on Audis, had a similar issue on my old Mini too. Pushing in should feel ok as you are putting positive pressure on it..but the return has a lot less pressure from the throwout bearing/clutch and return spring on the pedal.

Wiring looks good on both firewall and clutch, assuming that the other wire on clutch switch heads up to the ECU pin 39.