Fair or unfiar assessment

Right so I had this presentation today where I had to show how I would treat a person with a specific type of injury/problem. So, I was given a made-up case study where it mentioned what was wrong with the person and what 2 treatments I would use. I had to show this on a model (another person) who was pretending and acting out they had the problem on the case study. The whole assessment lasted 20 minutes whilst being video recorded where it was 15 minutes of demonstration of me demonstrating the treatment strategies so getting hands on and 5 minutes of question and answer and the assessor had a timer with them. This is where I was thrown back a bit because in my old similar assessment the timer was put for 15 minutes and then reset again for 5 for question and answer. However, in this assessment she put the timer on for the whole 20 minutes so when it beeped, I thought in my mind only 15 minutes were up and was preparing for the questions. She then said thank you and you can leave so when I said are you not going to ask me any questions she said oh you didn`t leave any time which was odd because another class mate who had their presentation before me said for him she set the timer for 15 minutes and then again for 5 exactly like my previous assessment. So, I`m worried because she might fail me or give me a very low mark (scraping a pass) which I think is unfair. What should I do?

Try to explain to her if you get opportunity; if not, find out if there's an appeals process but I'm not sure if you'd be successful. Honestly, my thoughts are that it might be best to have kept an eye on the time rather than just waited for the beep and given this, I'm not sure your attempts to raise your marks will end with the outcome you're looking for.

I know you have to keep your eye for the time, but I can`t be demonstrating and also keeping out for the time. I was already stressed when entering the room. Plus, the clock wasn`t facing towards me, it was on another wall where I would have look awkwardly and she faced the timer towards herself so I couldn`t see. I don`t get it though, why was the other assessment timer set for 15 minutes yet this one she sets it for full bloody 20 minutes? AND SHE IS THE COURSE LEADER!!!!.... It clearly mentioned that it will be 15 minutes for practical demonstrating and 5 minutes for question and answer and I don`t know what the hell she was doing. Uuuuugggghhhh I`m so p****d off. I hope I get a good mark.