Hydrocal is fairly easy to work with.
It is meant to be used as a slurry.
Did you use tepid tap water or hot water...hot water will shorten the soak time and quicken the cure.
It sounds like you may have been too excited and skipped the soaking stage...the soak is an important stage.
Measure 1:1, but do not just dump and mix.
In a third container, I like a smooth rounded bottom soup bowl as it has no edges and makes mixing bien mieux

Start with a small amount of powder in bowl, say a 1/5th or 1/4th, add some water and mix completely.
It will be loose, but it will be easier to mix if you have this loose plaster juice, add a little bit of powder to the loose batch until it gets thick, then add a small bit of water, just enough to loosen the mix...continue until all the powder is in the bowl, you can leave a little water out and add it as the mix soaks or saturates.
This hydration starts the process but let it sit for a couple minutes, keep slowly stirring, adding a touch of water (remember it was measured out so you can't add to much...it is how and when you add it) to keep it loose.
Then when it starts to feel like oatmeal, pour, tap to release air bubbles.
If you live somewhere hot and fairly dry, put it in direct sun, if not then in the sun on a shelf behind a window, or just let it set.
A fan on it will help pull excess moisture out and away.
If you find it too loose in the mold, pour it out into your bowl and add a touch more powder stir and pour again...keep in mind that this mix will be "hot" or curing so do not wait around, pour.
Best of luck and success
