Sweet & Savory Holiday Tart

There can be factors that can cause this, whether the air is dry or humid can have an impact. Because of this I always add the ice water or whatever liquid is called for in the recipe in increments. Maybe start with half the liquid, mix it and see whether or not you need more liquid, the dough should hold together when you grab some and press with your fingers. As Mrs Larkin said you can add more flour after the fact so it's not quite so wet but I find it better to add less liquid than called for initially and add more as needed.

I was just wondering what could have gone wrong because the recipe states mixing the dough it will be crumbly and not hold together and my dough was mushy

unless you've already baked it, pie crust is pretty forgiving. Mix in a tablespoon of flour to the dough if it's too wet. Inversely, if it's too dry, add a teaspoon of liquid until you get the consistency you are looking for.

Did you blind bake the tart shell?