Don't want to be mean but I find it a bit funny looking at this line. As far as I know, SQ will not changing seat assignment other than aircraft swapping or sudden upgrade on overbooked flight. I would say stay calm for now and check the seat map few days before your flight, there might be more seats opening up and you might find a better seats for you. You really shouldn't be mad at something that isn't yours to begin with.
Hope you have a great flight ahead.