Sorry to hear about your shower floor.
The proper mix for a dry pack is 4-5 parts clean washed sand and 1 part Portland Cement.
Mapei sells a ready mix which is just called 4-1. It is much stronger if you add the ad-mix for it.
Dry Pack can be walked on easily the next day and often sand can be swept off to a point. Sound like to me that you used either a ready made mortar mix (or thinset) and sand so your ratio of sand to cement is more like 16-1 which is not going to cut it I'm afraid.
Mixing dry pack is an art and you need to ensure you do it right. It is often advertised as an easy process but it is not if your not familiar with good mixing techniques or if you have limited tools at your disposal. A garden hoe and a clean wheelbarrow can pull it off. Best to make a small sample batch and hone your mixing skills before you go all in on your shower build. Dry Pack's should be 1 1/2" at the thin set point and reinforced with stucco mesh or the like. The should not bite into a wooden sub floor so a slip joint should be used. The heights and approaches vary depending on wood or concrete assemblies so check the TCNA, TTMAC or ANSI specifications for the right set up for your home.
We like to dry mix the sand and the cement very well. Take half the product and mix it on the wet side. Then we slowly add in the dry product until we have a good dry pack mix to work with.
Last year I started using mapei's Mapecem Fast Setting Screed Mortar and this is an amazing product. Just add water and mix. It is wetter than drypack and more user friendly. It can be covered with a sheet membrane the next day 14-16 hours.
Love the stuff.