I'm glad you're going to see the GP. It probably feels like they are over reaching their remit and perhaps even trying to put the brakes on a decision you've made very carefully with much thought and specialist input.
But, you don't know WHY the Gp wants to see you, and it's so easy to 'catastrophise' under these types of circumstance. I'd suggest going in and letting the gp have the conversational floor, and just listen until they've given you the information or questions they have for you. Say nothing and try not to cut them off, as that will just make you and the gp end up on opposite sides, where no sides need taking.
Then, you'll know what the fuss is about and can reply in a couple of ways that you can prepare before...
Either giving the GP more info on the situation and allaying his/ her concerns, or if it's new info saying thanks you'll take that jnto account as you move forwards (even if you don't think it's useful!), or if it's something that is over reaching and just annoying, smile say thanks and leave quickly to go swear somewhere out of ear shot! As if it's somethkng rubbish you'll be wanting to change GPs anyway and you shouldn't get stressed or upset trying to deal with it when you need to be focused on what's important in your life and positive for you 
Btw, Ive heard of stories where a GP has picked up on things that haven't been done properly by hospitals or consultants, and saved the day... Or some who let their personal prejudice and God complex behave terribly and do harm. There are good ones and bad ones and theres no need to stick with one who isn't going to be helpful. And I don't mean that you should blame a GP if they simply have a different opinion from you, but if their own limitations, assumptions or prejudices get in the way of doing a competent, professional, job, that's not good.
On that note, I'd class as very wrong indeed the GP who decided to tell an official body/ agency over the phone that 'I wasn't disabled at all, I just needed to mobilize more', that GP was a terrible GP! I wish I'd complained at the time, but as I was busy dealing with the sudden onset of a severely disabling life shortening condition, I couldn't defend myself. She almost derailed a vital process to assess my condition which was to access help for me, by her own odd attitude and unprofessional assumptions. To this day I don't know her reasons for giving that as her 'professional opinion', considering it was at odds with many consultants detailed letters and the basic medical facts in my health records. But it is a rare condition, so being generous she could have been simply ignorant, but then the professional course of action would have been to read my records, contact one of the many consultant im under, or simply admit she wasn't best place to answer the query and pass it over to another GP in the practice. But she decided to, and apparently told the professional on the end of the phone that if I really couldn't walk and was bedbound, which she doubted, I must have done it to myself by making myself deconditioned by refusing to do anything for myself, and that the best way to help me was to withdraw all care instantly! Luckily her ridiculous opinions were dismissed as they clearly had no basis in reality... Anyway I digress on my little rant!
Suffice it to say, if your GP is being that odd, I'd suggest moving GPs, but give them the benefit of the doubt and hear them out before you decide. Good luck.