Scaling up CFD position sizes without blowing up?

Hey everyone, been demo trading CFDs for a few months now, mostly on $DAX40 and some $SPX500, and I'm starting to get consistent. The biggest hurdle I'm facing now is how to realistically scale my position sizes. On demo, it's easy to just increase the lot size, but with real capital, the psychological aspect of bigger swings is hitting differently.

I'm using a fixed percentage per trade, but even then, seeing a larger number fluctuate makes me question my entries more than when the size was smaller. For those who've been through this, what was your process for increasing your risk without just jumping in and hoping for the best? Did you do it incrementally, or wait until you hit a certain profit threshold before upping the ante? Genuinely curious how others navigated this.