This is my first pregnancy, too. It was...not exactly planned, though we did plan to do it soon, so it's not like we were entirely unprepared and we did want to have a baby soon, so....yeah. Mixed feelings, which have largely resolved into feeling happy, but still sometimes mixed.
I talked to my sister-in-law and brother-in-law, who have a 2 year old. They planned their pregnancy and wanted it very much, but when she got pregnant, they both felt a series of mixed emotions. They felt mostly afraid, but also just overwhelmed and mixed up. I think it's also pretty normal to sort of mourn your "old life". The sister-in-law in question is also a doula, and she feels like it's very normal to go through a bunch of feelings. You don't have to feel guilty - it will help if you can stop beating yourself up for bad feelings, since you're just piling bad on top of bad, you know? Totally understandable that you'd be upset, but y'know.
It's a big change you're looking at. It's something you wanted, but now it's real - and it's so big. For me, I had to allow myself to feel overwhelmed, sad, scared, question whether this was what I really wanted, etc. before I could come to acceptance and then happiness. I think, if you can allow yourself to work through all the feelings without judgment, you'll feel a little better. You're not a bad person for feeling this way, it's a totally reasonable reaction to a big and overwhelming change in your life.