That's definitely an awkward situation. If you feel comfortable doing so, I'd definitely recommend speaking up in the prompt discussion.
Like, if someone comments trying to tack on a kink you're not into on your prompt, you could say "OP here - I have to admit I'm not actually into that kink, but if a filler wants to use it I totally understand. But could I ask that the kink be warned for if it does end up in the fill? Thanks." It's polite and let's the filler know your stance without stifling anyone. The kink you don't like might still be in there,but at least you've made yourself clear.
Alternatively, if people are headcanoning in a way that doesn't fit with your original prompt or even flatout derails it, you could say "OP here, love seeing all your headcanons. Unfortunately they might not really mesh with the prompt I made, but you should absolutely use them to make a new prompt, I'd love to read it!"
(Yeah, I've had to make similar comments on other memes so I've thought about this before.)
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Like, if someone comments trying to tack on a kink you're not into on your prompt, you could say "OP here - I have to admit I'm not actually into that kink, but if a filler wants to use it I totally understand. But could I ask that the kink be warned for if it does end up in the fill? Thanks." It's polite and let's the filler know your stance without stifling anyone. The kink you don't like might still be in there,but at least you've made yourself clear.
Alternatively, if people are headcanoning in a way that doesn't fit with your original prompt or even flatout derails it, you could say "OP here, love seeing all your headcanons. Unfortunately they might not really mesh with the prompt I made, but you should absolutely use them to make a new prompt, I'd love to read it!"
(Yeah, I've had to make similar comments on other memes so I've thought about this before.)