The hangers that bolt to the trunk floor can be moved side to side. If you still need to move the tips some more, loosen the clamp infront of the muffler so you can turn it slightly. That will move the tips.
I'd remove the tips until you get the valance on. Then you can adjust the hanger possition and/or muffler to get the tips to fit. You shouldn't have to take the car back to the exhaust shop.