Gareth. It doesn't matter whether or not you say it to a date's face. Or whether you tell them you're on Medium. If you put it online at all, you're visible.
Even so, you're thinking it too. She's going to know something's off, even if she doesn't know exactly what.
It's worth you feeling insulted if it rattles you out of this horrible thinking pattern you're trapped in.
Seriously. Snap out of it. If you go through with your plans, you're not likely to get a do over.