I did k12 last year as an independent purchaser of the curric -- not through a virtual school. I soooo feel your pain. I felt overwhelmed -- and I wasn't even accountable to a teacher!
Here's my practical advice: if you can "assess" out of a lesson, go for it. By that I mean, go right to the assessment and see if the child can master it at 80%. If not, then go back to spend time teaching the lesson.
Here's my mental health advice: relax. Easy for me to say, right? But seriously, try to settle yourself. It's totally reasonable to feel overwhelmed -- this is all new to you, right? Don't feel shame because the learning curve is HUGE! Be your best advocate and get the help from your teacher.
Finally, my Plan B advice: maybe this isn't the best fit. By all means, give it a few weeks to get a handle on it. But there's no shame in letting go of it if it's interfering with your life, rather than enriching it. Looking back, I wish I would've tossed the curric and gone with my Plan B: just math, writing, all kinds of reading, and play with my kids rather than put our family through agony by sticking with k12 when it just wasn't the best fit for us.
Best wishes!