You're feeling overwhelmed and having cold feet - I did too. Came very close to pulling out. I would have regretted it hugely though.
She's 10 months now and the first few months were in at the deep end/world upside down/omg what have I done - now she is a treasure and we wouldn't be without her.
What helped me feel calmer was the realisation that if we really couldn't cope, we know two excellent breed-oriented charities who have a large number of vetted homes, in case we decided to re-home. That took the pressure off. A plan B. (She's a working line Springer, so I had constant fears I wouldn't be able to give her what she needed - has turned out fine though. Have brought her up to be calm and relaxed, with plenty of fun, exercise and training, to fit in with our family).
Also doing 12 weeks of training in a small group from when she was 6mnths helped with structure and guidance to training, which helped both if us (mainly me) feel more on top of things/like I had direction so I relaxed a great deal and that has helped.
The puppy survival thread here is really supportive, and I recommend the FB group 'Dog Training Advice & Support'.
I always wanted a dog, and I'm really glad we did it.
At first, the children gave her a wide berth unless she was very sleepy and cuddly, but that's changed as she's settled down and they play together much more nicely now. She's been positive for all of us.
Best of luck x