ANSWER: I can understand how important it is for you to be identified in your correct gender, especially after coming-out, which can be an emotionally tough experience. The coming-out bit can seem for some, like the last piece of the jigsaw, although there's still a whole load to complete before you get near to seeing the full picture.
It sounds from your question that your mam is really trying, and you can see that. You may have had several years to realise and accept that you're transgender. You would've learnt all the terms, labels and lingo. You may have met other transgender people and belong to a community that have similar experiences to you, and have felt supported by them. When you tell a parent, their journey starts at that point - they have lots to learn and accept.
Very few parents imagine that their child could be transgender, even those that question their child's gender expression can be confused, angry and upset. You may have seen some of this present itself in the days, weeks and months after coming-out.
Being referred to as your mam's son is confirmation of your gender, and I get that. I remember after coming out to my parents, and the initial, 'what will the neighbours think' conversation, my mam would introduce me to her friends as 'my gay son'! It did feel uncomfortable, and I recall giving her the side-eye, though she was doing her best to be accepting, and finding her way in a world that she knew nothing about. So, what you think is not fully accepting could be your mam's process of learning, and maybe even pride in you, her son.
You could help your mam by encouraging her to ask questions, and allow her to make mistakes. Just like my job as a therapist, working with gender identity issues doesn't make me an expert - I have no lived experience of being transgender, and sometimes I'll make mistakes. The important part is that we correct our understanding and respect what it means to be a transgendered person.
There's a great charity called Mermaids, and they support both the child/young person and their parents - you're possibly older than a young-person, though the advice for parents is very informative and helpful. You may be positively surprised at how well your mam embraces these conversations - you've got this!