Erm, at the risk of pointing out the obvious, she doesn't have a grandchild yet - if you'd actually had the baby and he still hadn't got round to telling his mum, then yes, you owuld have been reasonable to do this. But at 10 weeks, before you'd even had the 12 week scan, really early. You clearly didn't contact her because you wanted her to know, you wanted her to pressure her DS into being supportive, or to get her excited.
As someone who's had a miscarriage at 11 weeks, I strongly, strongly recommend you don't tell anyone else until after your 12 week scan unless they are someone who you would want to support you/support your 'D'P if it was bad news at the scan.
I do feel for you, if you are feeling pressure from your DP to abort, then I can see why you'd want to make it "real" by announcing early, the logic being the more people who know you are having a baby, the harder it is to quietly have an abortion and move on.
However, now keep it quiet, get your booking in appointment with the midwife, get your scan date through. There's a good chance you'll be doing this on your own, think carefully about if you can do this on your own, it is highly unlikely you can strong-arm him into being supportive, no matter how much you want to.
Think carefully, your relationship with your DP is probably over with now, if you did abort, you'd hate him for it and no relationship can survive that, if you go through with the pregnancy against his wishes, he might stick around for a bit, but don't be surprised if long term it doesn't work once the tough parts of parenthood kick in. Is this something you want to do on your own?