Hmm, the whole order of authors thing is a bit of a contentious issue (mind you, in science, last position tends to indicate head of group!). Can you not discuss your concerns directly with your supervisor? You don't have to be confrontational, you could just raise the issue by telling him/her that you are keen to publish your results and ask for some advice about which journal to target etc. But don't worry about not being able to publish data that has been presented at a conference, that's certainly not a problem.