Most sri lankan/Indian grocery stores will have rosewater essence/flavouring. (star brand). you also get the "queens" brand rosewater in the super markets in the isle where they sell cake ingredients, colouring etc.
I make a lot of pound cakes. far too much of baking powder in this recipe. I would add only 4teaspoon baking powder for this quantity of flour - for sure. (also about 8eggs) failing which check your oven door beading (rubber strip) 2 tablespoons of Vanilla????? 2tsp (teaspoons) should do. there is far too much of liquid. one cup milk is more than enough, in my opinion. What temperature are you baking it at and for how long? I would say 180 degrees. I would bake...
When u take the cake out of the fridge give it a quick thin coat of icing, so that ur rosettes have something to hold on to. sometime back a similar thing happened to me. the icing on the cake was dry and the moment I studded the cake with bc stars, it kept falling off. this may be the problem. OR yr icing is too soft. whats the temperature over there. high humidity?
When I don't know how much of batter I need for a particular pan, I place the pan on the scale , set it to zero, pour water to the brim of the pan , and then divide the weight by 10. I make mostly butter/pound cakes/chocolate cakes. i.e if the pan hold 2000gms divide by 10 = 200gms x 4 (egg,flour,butter &sugar) that particular pan can hold upto 800gms of ingredients approximately.