Excel Formula to regression fit Cubic polynomial

You're doing the regression four times, which is Excel abuse. Select I34:L34, paste

=LINEST($G9:$G22,$F9:$F22^{1,2,3})

... in the formula bar, and confirm with Ctrl+Shift+Enter.

For whatever reason, charts and LINEST do polynomial regression differently. The chart gives R2 of 0.9843, LINEST 0.9697