**Neither a teacher nor a native speaker.**
Your choices seem good to me.
However, I have a problem with "thought".Are you fully sure the word belongs there?
Something like "because" would make more sense in my opinion.
I haven't gone to the fairground for ages because I don't suppose it has changed very much since my parents took me there back in the 1980s.
What do you think?
And who says "haven't gone" is wrong?
Another option would be "I haven't been going", but I don't see a reason not to use "I haven't gone".