why is \$|V_C|=90\$, not \$70\$? series RLC circuit
The voltage across the capacitor and the voltage across the inductor are 180 degrees apart hence when you calculated the voltage across both (\$X_L + X_C\$) to be 80 volts, that is the net voltage and, the capacitor voltage is in fact \$V_C\$ is 90 volts.

If voltages are 180 degrees apart and are in series then the net effect is one of subtraction.

Rough simulation:



Peak capacitor voltage (blue) is about 90 volts and peak inductor voltage (red) is about 10 volts but, importantly, they are anti-phase and their net effect, in terms of voltage is subtractive.

Circuit simulated: