Probalbly about 100. You might be right. I am a long term iron sight shooter
I've seen this many times before. Long time iron sight pistol user tries red dot sight without any instruction. He does what he knows: focus on the sight (dot in this case). The combination of focusing on the dot instead of the target and the "wild" movement of the dot makes him shoot slow as shit.
100 rounds are nowhere near enough to learn how to use one, and you really need some coaching even if it's online or self directed coaching. The alternative is wasting a bunch of ammo with no guarantee that you'll eventually figure it out.
This is magnified if your index is poor. By index I mean drawing the pistol while looking strictly at the target and have it show up right in front of your face with the sights on target. Basically relying on kinesthetic awareness and not your eyes to have the sights aligned and on target at the end of the draw.
You also need to get used to the fact that the dot is going to show you all the movement that has always been there but you couldn't perceive with irons. You need to get used to the fact that for most shots the dot doesn't need to be still. It all comes from putting miles through one.
Once you learn how to use one, an RDS on a pistol opens up another level of performance from where you are.