Don’t worry, I’m a senior developer too and if I can do it, anyone can.
Serious answer though: there’s always a lot of learning in the first few months of a job. You can be senior in one job but then walk into another and half the things you knew that made you senior in the previous job are no longer relevant. But that’s ok, you just have to be willing to learn.
New Balance do some of their models in 4E width (which I wear). Having said that, I think NB’s sizing runs very narrow in general, so 4E to me feels slightly wide rather than very wide.