Sorry to hear this.
I went through the same thing, found baby had very severe spina bifida at 21 weeks, would not have survived to term. There is some good advice on here about people to contact, things you might be feeling, but I thought I would share with you exactly what process I went through.
I found out on the Tuesday, had our (late) 20 week scan, was taken up to the foetal medicine place and they rushed about finding me a consultant to talk to, had to wait a while. He went through options, it became clear a termination was really the only one. We had to go home and come back the following day for a scan with the 'right' consultant, to doubly confirm the diagnosis and then to talk through what would happen.
They planned when it would all take place based on when they'd have plenty of staff and when nothing else planned was going on, initially the Saturday then they were able to bring it forward to the Friday.
At the second scan on Wednesday I was there a while, needed to talk it all through then I was given I think it was two pills to take at specific times over the next couple of days. I also had to go shopping to get anything I might need for labour as obviously I hadn't packed my bag yet or anything.
Friday morning went in for 9.00, had to wait ages for a consultant to come in and give me a pessary, then it was basically a case of waiting for things to happen. Midwives were absolutely fantastic, I was put in a room right down the end of the corridor right next to the loo so I didn't have to encounter any happy labouring women. Gradually got more painful, or 'uncomfortable' as they call it, I was sick a couple of times, had some pain relief, then it happened fairly quickly, was all over by about 4.30ish I think. I was able to hold my baby for a while, they dressed him and put him in a little tiny basket, we were given some photos and hand and footprints as well. Bizarrely as well as being obviously devastated, I felt happy as well, when I was holding him, I felt lucky to have been a mum even though he was no longer with us.
I'm crying now, sorry. I just thought that the exact detail of what is probably going to happen might help you, it would have me, I was terrified of labour and those couple of days when I was still pregnant waiting for it all to happen were terrible.
A midwife came to see me the following day at home, I was in a pretty bad state for a while, but it does get easier I promise you. Anniversaries are a bit tricky, try and let people help you if you can, I shut everyone out for a while.