✤.J.
Let me start by saying congratulations & that I commend you for not freaking out.
I found out I was pregnant with my youngest when my oldest was 10 months old, as well, so you're in good company. ;)
I'm not going to lie & say it'll be easy-peasy, but I will tell you that you absolutely CAN do this & it likely won't be nearly as bad as you're thinking it will. I had my kids do a lot of milestones together to simplify my own life such as potty training, for instance. That meant that my oldest was a little late & my youngest was a little early, but it worked for us.
Now they're 12 1/2 & 11 years old (next week) & while they are certainly not the best of friends at this stage, I'd not have it any other way. They're close enough in age to be going through a lot of the same issues at the same time & share some friends, but far enough away from each other (2 years difference in school) to be able to do their own things & have their own clear-cut identies.
I know it's easier said than done, but try not to stress about it. You're in the situation now & it'll all work out just fine!