Heatmap like plot with Lattice

Heatmap like plot with Lattice

I can not figure out how the lattice levelplot works. I have played with
this now for some time, but could not find reasonable solution.
Sample data:
Data <- data.frame(x=seq(0,20,1),y=runif(21,0,1))
Data.mat <- data.matrix(Data)
Plot with levelplot:
rgb.palette <- colorRampPalette(c("darkgreen","yellow", "red"), space =
"rgb")
levelplot(Data.mat, main="", xlab="Time", ylab="",
col.regions=rgb.palette(100),
cuts=100, at=seq(0,1,0.1), ylim=c(0,2),
scales=list(y=list(at=NULL)))
This is the outcome:

Since, I do not understand how this levelplot really works, I can not make
it work. What I would like to have is the colour strips to fill the whole
window of the corresponding x (Time).
Alternative solution with other method.
Basically, I'm trying here to plot the increasing risk over time, where
the red is the highest risk = 1. I would like to visualize the sequence of
possible increase or clustering risk over time.