so im in 1st campaign, original fallen enchantress campaign map 2. the mission was to build boat and cross the sea, on a my way i met this character, darwella who gave me quest, i accepted the quest but then realised that she took my last spot 5/5 in party. so now i cant board the boat so i cant leave and i cant detach heroes in this campaign. i just dont get it, all heroes that i have with my right now are mandatory exept for two, 1) relias 2) rihossa 3) umana ferensu + 4) gnarl i recruited in 1st mission and this 5) darwella. so no i have to ask was this poor design issue? because to be completely honest, if had to stumble upon random npc with a quest i would surely accept it, i wouldnt even pay attention that my all slots would be full. and now im in a situation like this, i cant leave this damned island. please help.
im just a newb here, maybe there is a simple solution which i dont see. here is the screnshot.

http://img541.imageshack.us/img541/3580/pr9w.jpg