Passive Attenuator + Level shift simulation slightly off from hand calculations not sure where mistake is
You're just wrong with voltage dividers, twice .
In the beginning, if you have to map 7V peak to peak onto 2V you need a 1/3.5 voltage ratio that turns into a 2.5 resistance ratio, i.e. R2=20ohm.
Then on the Thevenin voltage V1, you have the same voltage divider but upside down and so
$$V_1\frac{R1}{R1+R2}=1.65\,\mathrm{V}$$
$$V1=1.65\,\mathrm{V}\times\frac{7}{5}=2.31\,\mathrm{V}$$
From now on you should only design R3/R4 divider to have 20ohm and 2.31V Thevenin equivalent.