By default, the chart series will be drawn to fill as much of the plot area as possible, which is why you are seeing the behavior you describe. shinobicharts offers a number of ways in which you can prevent your upper tick mark label (in this case, on your y axis} being partially obscured.
Firstly, you can ask the chart attempt to show a data range of your choosing. You can do this by setting a default range (crucially) before you load your data. Alternatively, after your data has been loaded you can request that the chart display a given range. In both cases this would be done on your axis and you would most likely choose a range which was slightly greater at its upper boundary than your data.
Another option you have is to set an upper range padding on your y axis. You would need to provide a value that is just great enough to prevent the upper tick mark label (on the y axis) being partially obscured.
Finally, a further option you have is to set the high clipping mode of the tick marks and labels (on your y axis) so that any tick mark label will never be partially obscured.
Details of these various methods can be found in our api docs which can be found here:
I hope that you find this helpful.