I'm in the same situation with UCL. Everybody else thinks I'll get the grades, but I'm actually being realistic, not pessimistic, when I say I'm not. However, do you trust yourself? I trust myself that, no matter what my grades, I'll get into uni. Whether that means a slightly different uni or a foundation year, who knows. But I know that wherever I end up going to uni, I trust myself to be happy and succeed there, and if I'm not happy, I trust myself to maybe transfer or work hard to do my Master's elsewhere.
Good luck! Hope to see you there!