JMP automatically centers variables when higher order terms are added to the model. This practice is recommended to reduce the collinearity among predictors to, in turn, reduce the variance inflation. (x^2 is highly collinear with x otherwise.)
There are two ways to get the form that you want:
Fit Using the Uncentered Variable: Click the red triangle next to Bivariate Fit and select Fit Special. The option to center variables is near the bottom. Here you can also select the second-order polynomial model to be fit.
Convert the Model Afterward: Save the equation as the prediction formula. Open the formula, click the red triangle and select Simplify.