Just diagnosed, but masked a lot, so people aren't believing it (and I'm struggling to ask for help)

I was only diagnosed last week and since then I've told my family, none of whom knew I was being assessed. There was an initial mixed reaction but I've since been able to allay any concerns and misconceptions (particularly amongst my grandparents who thought I was joking) and they've all now accepted it. 

However, at work, it's proving more difficult. I decided to tell my manager and their boss (they work quite closely). In both cases, they both said "based on your interactions with us we would never have suspected, but if the doctors say it's that then it must be". I might be reading into it wrong, but it seemed like they didn't want to believe it. My line manager also said that I interact well (though I know it's due to masking!) so they told me to "continue whatever I'm doing to cope". I tried to explain that I have masked my autism a lot up to now but my manager seemed to take that comment the wrong way and it felt like I'd been deceitful and purposefully hiding something from them. I tried to explain some of my traits to help them understand, such as scripting conversations but that didn't quite get the message across as my manager said he "prepares a few bullet points before meetings" and that "in 5 years time when you have more confidence, you might not need to write everything out". My manager might be right - but I've done this for 22 years, I can't see it suddenly stopping once I reach this moment of "confidence" that everyone seems to expect will suddenly happen to me.

I might be being overly sensitive but the comments that I got at work on this have made me really question what I should do next. My work environment was the key reason why I pursued a diagnosis because it was draining me. But the guilt I feel now at trying to ask for any changes, especially as the diagnosis has taken 12 months to get, within which time I suppose I could have said something to work - it just leaves me in a tricky situation. 

Am I being silly with the comments I received or is this expected? I personally am so happy to finally have answers to a lot of things, but the perception of others and as I try to 'unlearn' the things I have masked just seems impossible, even though I know I need to do it to stand any chance of having energy left at the end of the day (something which has been significantly lacking over the last week since my diagnosis!!).

Any advice or 'unmasking' experiences would be really, really appreciated. Thanks everyone.