Definitely give yourself grace and don’t be hard on yourself if you feel like you aren’t giving anyone your best at times (and take the advice to just aim for B/B-). My son is almost 5 and I still haven’t completely mastered the whole working mom thing—guilt is just a part of it (or it is for me at least).
If I’m being completely honest, I was a mess the first few months coming back and I was just up front about that with my boss (thankfully also a mom and understanding). I did what I could, generally kept the wheels from completely falling off, but that was about it. I was probably squarely at C level for me.
I had 14 weeks, so slightly more than three months, but that is not long enough for maternity leave. Your body/mind aren’t yet completely back to normal, your baby is changing and growing every day, and it’s also just exhausting to be a parent of an infant. There’s a reason why many countries give 6-12+ months for mat leave.