Chocolate mint ganache - too runny
I think you've got too much liquid in your ganache, either because the chocolate or the glucose syrup (assuming its syrup). Milk chocolate can be used in a ganache but as it has a lower proportion of cocoa you would want to use less cream in your recipe when using it. 

You could try whipping it as the inclusion of air should thicken it, however that will change the consistency so it won't be smooth and glossy. I would suggest you reheat it and melt in another 30 grams of good quality dark chocolate or so. That amount is not exact or based on any sort of science on my part, more instinct from previous ganache making experience. You might need to add more depending on your circumstances.