Cultural differences

Ohh, now I’m struggling again… The more time I spend here the more I grow into the culture. However, that also means that people start to treat me more and more like a Korean an expect me to know all the unwritten rules. One of the things I’m really struggling with is schedules between my host family and me. We are both very busy, and don’t have too much family time together. However, in Finland you plan things well in advance where in Korea you are more spontaneous. Today I faced this fact again when I had already made an appointment with my Korean friend for the evening. However, in the lunch table the family told that we are going to do something together in the evening.. I felt so bad and tried to tell that I already have appointment and it would be extremely rude to cancel it, but I feel that the family didn’t quite understand it. They tried to say I should cancel the dinner with my friend, but then again, I just confirmed in the morning that I will join them and they will pick me up with car at 6PM… I have had this problem so many times before, too, and I have tried to tell politely that I will arrange time in my schedule if they just tell me a few days before. However, still after 2 months they try to find hints in my speech instead of asking directly and then we end up in the cultural crash. I might have an appointment made a week ago, and then on a Saturday morning they might have everything planned for the day. When I mention that I have other obligations, they are surprised because they thought I’m free and found it unnecessary to ask… And of course I end up feeling so bad… From now on I will try to ask them more about their plans and tell about mine, so that I don’t have to disappoint anyone… =(
My Asian friends, do you have any suggestions?