You have all the time to rearrange or polish your flower arrangement. The flower design should look beautiful and artistic enough before you place your filler, when the filler is already placed, it would be harder to move your things around the area or place. Bear in mind that The filler are very fragile.
Next, fill your "real" vase about two_thirds of the way with warm water. Make sure it doesn't leak. Add flower food if available. (Follow the instructions on the packet.) Place a few of your larger blossom flowers in the vase and step back. This will give you a better idea of how to proportion your bouquet. If the stems are too long, simply cut them shorter. If they are too short, try a different container, or add pebbles or marbles to the bottom of the vase to elevate your flowers.