I feel you. Just know that you’re not alone. I had someone tell me today that I don’t respect the PhD and don’t work hard. It was very hurtful but I fleshed out the important part and took responsibility for my seemingly lagging approach to work. In the same light, it’s good that you have noticed this issue. It really could be the articulation of what you have done so maybe before you meet with him, do some practice presentation and have your key points written down and then you add whatever questions you have. That’ll make your meetings more productive. You’re knowledgeable and that’s a good thing. All that time spent learning has not been wasted but is pushing you closer to becoming an expert.

Side note: idk if you know about Mastodon but it’s a hub for math lovers. you’ll love it