Regression coefficient is zero

I am trying to construct a quadratic regression model for a data as

$Y={\alpha}_{0}+{\alpha}_{1}{X}_{1}+{\alpha}_{2}{X}_{2}+{\alpha}_{3}{X}_{1}{X}_{2}+{\alpha}_{4}{X}_{1}^{2}+{\alpha}_{5}{X}_{2}^{2}$

I am getting coefficient of ${X}_{1}^{2}(\to {\alpha}_{4})=0.00000006\approx 0.$. How can we interpret this model for ${X}_{1}^{2}$ term? What is the impact of ${\alpha}_{4}=0$ for the model? Adjusted ${R}^{2}=0.9988$

I am trying to construct a quadratic regression model for a data as

$Y={\alpha}_{0}+{\alpha}_{1}{X}_{1}+{\alpha}_{2}{X}_{2}+{\alpha}_{3}{X}_{1}{X}_{2}+{\alpha}_{4}{X}_{1}^{2}+{\alpha}_{5}{X}_{2}^{2}$

I am getting coefficient of ${X}_{1}^{2}(\to {\alpha}_{4})=0.00000006\approx 0.$. How can we interpret this model for ${X}_{1}^{2}$ term? What is the impact of ${\alpha}_{4}=0$ for the model? Adjusted ${R}^{2}=0.9988$