AIBU to say no?

[Hoppinggreen]

I am a school Governor and have run a few (voluntary) sessions at a couple of schools in an area where I have expertise and they have all gone down really well so I offered to do them at the school where I am Governor
Imagine that I offered to do a session on Coding and another Governor offered to do a session on Computer hardware as an analogy
The HOY has come back to say that they would love a session on Computer Hardware and can we both come in and run them on these dates. I vaguely know a bit about hardware where it impacts my area but not much and as the other Governor knows all about it I suggested that as it wasn't my area I probably couldn't add anything but I hoped the sessions went well and if they DID want to cover Coding another time and/or within the session to let me know
The HOY has now emailed me to say that it would be better if we could both come and the other Governor has offered to send me all her slides for the sessions so I can assist her. I know very very little about Coding and she is an expert so I have no idea why they need me
I am absolutely fine with not running the sessions I suggested but I really don't fancy giving up my time to sit like a spare part or hand out bits of paper or whatetever else when someone who knows even less than me about Coding could do it
AIBU to (politely) say no?

Just answer that you are willing to run your own course in your own field but have no desire to assist anyone else.

YANBU
You offered to do a session on coding. They don't want you to do a session on coding, that's what you offered and they declined. The end.

When the other governor offered to do the computer hardware session they didn't know or expect help from you so no need to give it in my opinion.

I have tried that, I got a "oh I am sure you will have some insights" (I won't)

If you need to reply, I'd say something along the lines of:
Dear Ridiculous request:
'As I said in my previous email, I'd be happy to talk on 'my expert area' but as this session isn't required, I will not be attending. If you would like it in the future, please let me know'

The person has absolutely no idea the difference between Coding and Hardware and there being two absolutely independent areas of expertise; probably lumping it all into "that fancy computer bumpkin magictrickery"

Stick to your guns.

Tell her she is likely to have more insights so she can assist instead of you

Well its not actually Coding and Hardware, that was an illustration but I know what you mean

Its the other Governor not HOY who has said I can assist
Anyway, I have just said that I am not available on the dates suggested