Many online wedding gown retailers will offer alterations; however, you may be able to get a more precise fit if you have the alterations done by a local dressmaker who can measure you and make the necessary adjustments.
Your wedding planner, local dressmaker, or the store you bought your dress from should be able to point you in the direction of someone who can help.
In this case, try asking your dressmaker, or the shop you're buying your dress from, to give you a small swatch of the fabric as a sample.
The Dereon name is derived from her grandmother's name, Agnez Dereon, a Southern seamstress and dressmaker.
Good dressmaker scissors are a must for getting clean, straight edges on cut fabric.