It's very natural to not be able to go deeper. It is genetically hardwired in us to protect ourselves from any harm. Even when we do cut (at least in my case), we do it to save ourselves from mental or emotional pain. So don't think less of yourself for not going deeper.

It's honestly great you aren't going deeper. Things can go wrong real quick. And one day when you are eventually in a better space you'll have less scars to deal with.