The host insists a third time,and you could finally say yes and take a little. If you really don't want any more, take very little and leave it on your plate. It is the same with whatever you are drinking. During the meal, when your cup or glass is less than half full, your host or neighbor will refill it. It is polite to refill your neighbor's glass. This means that you should keep an eyi on your neighbor's glass all through the meal.
The most important place at a table is at the middle. An important guest will sit at the middle of the table on one side, and the host will sit at the middle of the table on the other side. This may be confusing when the table is round, but the Thai get it right somehow.