No, it's not your fork, nor your throwout bearing. If it was, you'd hear scraping noises. The slave cylinder's piston rod only pushes the fork forward, but the piston rod and fork are not actually connected together. Therefore, the fork can't possibly hold the pedal from returning back. Check for clutch fluid leaks. Either your clutch master or slave cylinder is the culprit- one of them probably has to be replaced. Or maybe you'll get lucky and it's just air in the system. In that case you'll need to bleed the clutch hydraulics.