Seeking balance

I have so many thoughts on this subject swirling around in my head, so this probably won't be a very coherent post. My apologies in advance.
My family leave time from work is ending this week and I recently told my boss that I can't go back to work full-time. It was a hard decision to make, in some regards, but I was also dealing with the feelings that it would be impossible to leave Katie for an extended period of time. I had the same feelings after Ellie was born, but this time around we were dealing with the additional incentive that almost all of my income would be eaten up by double daycare costs if I returned to work... so I'd have all the headache of the job without much financial gain. I asked about going down to part time, not sure how that offer would be received... but my boss agreed to the idea. So on April 2 I will go back in to work an evening shift, something I will be doing a few times each week. We're timing it so that I will go in after Brian gets home from work, thus eliminating the need for daycare. It will be a major cost savings and also enable me to bring in a bit of supplemental income. This is all good and it feels feasible. I don't think it will be easy to head into work after a full day home with the girls, but I am looking forward to using my job skills and having some adult interaction. Giving up my job (especially in this economy) was a tough and scary choice to make. But I remember so many feelings of guilt and regret when I went back to work just 9 weeks after Ellie was born. There were so many days when I felt like I wasn't giving my best efforts on the job OR at home because I was stretched so thin. I'm hoping to avoid that this time around.
But I still find myself doubting my efforts and worrying about the path I've chosen. Maybe we're still all in the transition phase AND things are still really hard with a new baby, but I often worry that I'm not doing a good enough job with the girls at home. I want to make sure Ellie continues learning and progressing, like she was at school, but it's tough to have the time or get the toddler's cooperation in doing any sort of "lessons" (like letters or counting or something of the sort) during the days. Katie's just along for the ride on everything right now, which sometimes makes me feel bad because I don't have the time to devote solely to her tummy time or motor skills or whatever else the parenting books (that I don't have time to read this time around) suggest she be working on right now.
I know we're only a couple months in. I know that some of this probably sounds dumb. I know that these girls are in great hands with me and Brian, and we're certainly not scarring them for life (so far!) I just want them to be exceptional. I want to fill our days with fun and learning and laughing, which often is a far cry from the scolding and disciplining Ellie requires these days.
I'm seeking balance. Maybe it will be a constant quest on this parenting journey. Right now I would love to know for sure I'm making the right decision for me and for our family. But instead I need to have faith and patience. Guess I should take some of the advice I've been doling out to Ellie on a daily basis -- be patient, settle down, don't whine and be happy.