check = (y~=0);
You don't want to check only for y actually touching the ground. If the ODE solver were to evaluate your function at time t = 1 (when your projectile is above ground level) and t = 2 (when your projectile is under ground level) but not t = 1.6 (when it exactly reached the ground) this events function would not detect the landing.
The ballode example has an events function you can use for this purpose. In fact, that example seems pretty similar to the problem you're trying to solve. You can open that example in the Editor and take a look at its events function.
You don't want your events function to return a logical value, you want it to return the height above ground and let MATLAB stop the solver when that height crosses zero (landing.)
