For some background: MC asked his girlfriend questions about wedding arrangements without specifying who the wedding is for (he's arranging his cousin's). Later, MC realises his girlfriend thought the wedding talk was about them the whole time:
I know that まさか is usually used to indicate disbelief, but I'm a bit torn as to whether here まさか would mean 'It probably wasn't that, right.' (disbelief, unsure that's what she thought) or 'To think that you had thought that.' (surprise, but realising that's what she thought).
I'm leaning towards disbelief, but I feel like that conflicts with his thought process all 'it's possible she could have thought--'
A second opinion would be much appreciated.