excel - Why do I get wrong prediction when using this polynomial forecasting formula -

i forecasting on growth per period.

i have formula of polynomial regression
y = -5e-05x2 + 0.0348x + 0.7148.

i translated to: =exp(-5)-0.5*(b4)^2+0.0348*b4+0.7148
b4 period running number (i have 365 days, b4 first period ,c4is next period etc)

i have strange results (my prediction decreases on time instead of getting increased) guess didn't interpret excel's formula well.

how can resolve problem?

an image of chart , excel's formula:

-5e-05 isn't exp(-5)-5

it -5 * 10^(-5)

for clarification: -7e-05 means: -7 * 10^(-5) = -.00007