We all feel that way La! I'm not even a single mom and I still feel like we don't spend a lot of time with our kids since DH and I both work full-time. Rather than trying to be "super-mom" every day, which is impossible for most or all of us, maybe try to carve out some special time every week - even if it's only for an hour or two on a weekend day. Plan something or just spend some time doing what he wants. I don't always succeed even at that but I do try to at least actively choose to say "yes" more often, instead of just always saying "not now, I'm busy." Like all last weekend, my son was asking us to do a "treasure hunt" he had planned, and my husband and I kept putting him off because we were busy with other things. I finally realized that I should stop just reflexively saying no, and you know what? It took literally about 5 minutes and made him so happy.
I was brought up mainly in the age of what I heard someone call "benign neglect" -- where our parents basically just told us to "go out and play" and didn't spend a whole lot of time agonizing over "quality time".
I turned out ok and don't resent my parents for it. I do remember the fun times we spent together, playing board games or doing stuff on weekends, but believe me, they didn't spend a whole lot of time planning activities or learning experiences! I think we are too hard on ourselves these days!E
ETA: oh, and I think that trying to do a whole day devoted to your child is admirable, but way overeaching. I don't know of many adults who can do that regularly and stay sane.
My son would have us playing Pokemon all day, for example, and my limit on that is about a half hour.