Royal icing too thick?

I used Wiltons recipe- 4 cups confectioners sugar, 3 tablespoons of meringue powder, and 6 tablespoons of warm water. But when I tried to make some flowers but it was hard to squeeze and was really difficult. Do you think it was too thick? Should I have put a little more water? Also is sifting the confectioners sugar really necessary?.. I didn't because I don't have a sifter. Maybe I didn't mix it up long enough? I have a hand held mixer. Please anyone with advice or what could be the problem please help! Thank you!