Try laying a large blanket on your dining table. Use some spray sizing (or starch) and lightly spraying and ironing the top with a DRY iron....no steam. If that doesn't work, then try steaming. If you're taking it to a longarmer they may be able to work out the areas that don't lay flat.
![Smile](https://cdn.quiltingboard.com/images/smilies/smile.png)
Laying it out on a table gives you more flat area to help.