Don't worry too much about it, my advice would be to do what you can and present that. I've presented incomplete work at a conference and have seen some were things didn't work out and it was more a 'this is not the way to do this experiment' type talk. At one small conference I went to I had to change the topic at the last minute and emailed the conference organiser (who happened to be someone I knew) to check it was ok. They were fine with it and actually told me they had a few cancellations and much preffered that I had actually done a talk than nothing at all. Just be honest about it and say you have more interview planned