Did I mess up house training?

Puppies don’t have full bladder control until 4-6months so I figured leaving the pad down would be okay but now I’m thinking I screwed up. He has accidents and he is 13 weeks so I figured leaving the pad down would make it better. Is it too late to house training him still?

He doesn’t pee in his crate and will hold himself but in the house he just goes, and not sure what to do. I’ve been teaching the bell, and he uses it but he thinks it’s for treats lol. We also have the issue with stairs. I live in an upper unit and he is scared of the stairs which I think is delaying the training as well.