Sage interact: Label of slider control is cutted

edit

1) When the label of a slider control is longer than ca. 15 characters, the label will not be displayed in full length. How can I get the complete string being displayed? Here is a working minimal example, where only "This is par..." is shown.

2) And an additional question: Is there an option to place the slider and its label left-aligned, centered or right-aligned?

@interact
def myplot(a=slider([-5..5], default=2, label='This is parameter a: ')):
    show( plot(a*x^2,(x,-2,2)) )