Really sorry to hear your bad news :( I went through a missed miscarriage recently myself. It's upsetting when you thought there was nothing wrong. I really feel for you. There is a lot of good support on these boards. I found the miscarriage / pregnancy loss board more helpful than any other info I could find online or from the hospital. In case you don't get time to read it, I'll give you some of my experience here if that's OK. I think it's best to be prepared.
If you have a good relationship with your family, it's best to tell some of them what you are going through. Having a miscarriage is upsetting and painful. Please don't go through it alone. Also, it goes without saying but you and your partner need to be kind to each other now more than ever.
Be prepared to stay at home for a few days during the worst of it. I hope you can take some time off work. Have some thick pads for when the bleeding gets very heavy. I used Tena Lady Silhouette pants which were great. I stayed in my pyjamas, ate chocolate and did whatever I could to distract myself - trash TV, books, games, whatever keeps you occupied.
At some points the cramping got intensely painful and I could do nothing else but wait for it to pass. That pain came and went throughout the day. I think I bled for about a week altogether with 2 days of really bad pain. Some women bleed for longer.
After I passed the sac I felt physically better. I couldn't see the baby, just the sac it lived in. In a way I was glad to see it. I buried it in my garden and we sowed some nice flowers over it later. You may prefer not to look at all or do anything in particular with it - just have a think about that now as you may need to decide quickly later. Even if you decide to flush it, it will end up in the sea under the stars.
After the miscarriage you'll still feel sad for your loss, but you will feel much better about it than you do now. Your hormones will settle and you'll be able to mentally deal with it. Take a pregnancy test every 1-2 weeks. Once you get a negative test you can try again if you feel ready.
Most women who miscarry will have a healthy pregnancy later. I am pregnant again 2 months later and hoping for the best. I really wish you the best and I hope this difficult time passes quickly for you. Thinking of you.