No, you have not stuffed your chances. This is only one assessment task. Compare your mark to others in the class. They may have done equally badly. If not, then you need to put in extra work for the rest of your assessment tasks to bring up your class rank. How much of your final mark was this assessment worth? If it's only worth 10-15%, then you haven't badly burned your UAI prospects. It's not the end of the world since you have another 3-4 assesment tasks to go, with the Trial usually being worth the most. Also, if you're doing more than 10 units, you have a buffer.
I_F