Estimate the integral with Trapezoidal rule: $\displaystyle \int_{-1}^2 x^2 dx$

$\displaystyle \Delta x = \frac{2 -(-1)}{4} = \frac{3}{4}$

$\displaystyle x = 0, y = 0; x=.75, y= .5625; x=1.5, y= 2.25; x=2.25, y=5.0625; x=3, y=9$

$\displaystyle T=\frac{\Delta x}{2}(y_0 + 2y_1 + 2y_2 + ... + 2y_{n-1} + y_n)$

$\displaystyle T = \frac{3}{8}\left(0 + 2(.5625) + 2(2.25) + 2(5.0625) + 9\right)$

$\displaystyle =9.75$

Now when I integrate this I get an answer of 3. Now what the heck is going on? My percent error is over 200%.I've done these problems a lot yet this one I keep getting way above the exact answer. Something is wrong here. What did I do wrong? It's driving me mad