Hello! First off, you haven't done anything wrong. There are all kinds of issues that can affect plants that are outside of our control. for your situation with this spruce, there are a couple of things to look for:  

1) I know you say that you are watering, but overwatering can also be an issue, so before you water again stick your finger into the dirt and make sure it really needs the water.
2)spider mites might have invaded your tree. Hold a piece of white paper under a branch and give the branch a shake. Check and see if any little tiny spiders fall out. Here is a fact sheet about spider mites:  https://extension.colostate.edu/topic-areas/insects/spider-mites-5-507/

3) here also is a sheet about spruces and what might be attacking them.  Take a really close look at your tree and compare to the pictures here - that will probably give you a good idea of what's bothering it.  https://web.extension.illinois.edu/plantclinic/downloads/Plant%20Clinic%20Report%20Spruce.pdf