Hi, erm its impossible for me to say whether you'll be accepted if you slip a grade. It just depends on how many offers the uni has made compared to the number of places available. When I started back in 2007, I know of people that got in with BBC.
I'm due to graduate with a B.Eng this July. The course has been quite intense, especially the final year when most of your time will be occupied on your design project. It is split into two parts, a group project, then an individual project. Other than that, all I can advise is keep up-to-date with your work, attend lectures, attempt tutorials..... and seek advice if you don't understand anything (especially in 1st year when you learn the fundamentals, which you then build on in 2nd and 3rd year). Doing a placement year is also highly recommended, around half of the students choose to do one... You'll be told about it when the time comes, and theres plenty of support available.
Good luck with your exam results, hope it goes well. If you have any other specific qns, feel free to ask =)