Rookie Mistake

Yes absolutely you can add more. You can even add it just as soon as the open time is up if need be. I've added more before the open time was over and long after the cure time is finished and never had a problem with the bond. Though the best bond is using the same silicone as the first pour but in a pinch, different types can be added one on top of another - just be aware that different densities of silicones can be separated sometimes with enough force.

Not such a rookie mistake, I'm a veteran of using these silicones and I've done the same thing a few times myself so don't be too mad at yourself.