Plotting a corrugated ribbon on a 3D Plot

I was assigned to write the following code:

Clear[P, t]; 
P[t_] = {-t, t, (1/2) t (8 - t)}; 
arch = 
  ParametricPlot3D[P[t], {t, 0, 8}, 
    Axes -> Automatic, AxesLabel -> {"x", "y", "z"}, PlotRange -> All, 
    Boxed -> False, ViewPoint -> CMView, BoxRatios -> Automatic]

The output from the code is:

I was then tasked with obtaining the unit tangent vectors, the unit normal and binormal vectors with the following code:

Clear[P, x, y, z, t, unittan, mainunitnormal, binormal]; 
P[t_] = {-t, t, (1/2) t (8 - t)};
curve = ParametricPlot3D[Evaluate[P[t]], {t, 0, 8}]; 
unittan[t_] = P'[t]/Sqrt[P'[t] . P'[t]]; 
unittanvectors = Table[Vector[unittan[t], Tail -> P[t]], {t, 0, 8, 0.5}]; 
mainunitnormal[t_] = N[unittan'[t]/Sqrt[Expand[unittan'[t] . unittan'[t]]]]; 
mainnormalvectors = 
  Table[
    Vector[mainunitnormal[t], Tail -> P[t], VectorColor -> Red], 
    {t, 0, 8, 0.5}]; 
binormal[t_] = N[Cross[unittan[t], mainunitnormal[t]]]; 
binormalvectors = 
  Table[Vector[binormal[t], Tail -> P[t], VectorColor -> Red], {t, 0, 8, 0.5}]; 
everything = 
  Show[curve, unittanvectors, mainnormalvectors, binormalvectors, 
    ViewPoint -> CMView, PlotRange -> All, BoxRatios -> Automatic, 
    AxesLabel -> {"x", "y", "z"}]

which produces the following plot with vectors:

I am now asked to plot a ribbon two units wide whose center curve coincides with the curve plotted above. Corrugate the ribbon if possible. The hint that was provided was to use binormal[t].

One of the plots I produced was using the following code:

ParametricPlot3D[P[t] + s mainunitnormal[t] +  Cos[3 s] binormal[t], 
  {t, 0, 8}, {s, -Pi, Pi}, 
  PlotPoints -> {15, 15}, ViewPoint -> CMView, BoxRatios -> Automatic, 
  AxesLabel -> {"x", "y", "z"}]

Is my plot in line with what assigned task demands? Also, how can I go about ensuring that the ribbon is only two units wide?

Clear["`*"];

P[t_] = {-t, t, (1/2) t (8 - t)};
curve = ParametricPlot3D[Evaluate[P[t]], {t, 0, 8}, 
   PlotStyle -> {Thick, Red}];
{unittanvectors[t_], mainunitnormal[t_], binormal[t_]} = 
  Last@FrenetSerretSystem[P[t], t];
solid = P[t] + ({0, s, Cos[3 s]} + {0, 0, h}).{unittanvectors[t], 
     mainunitnormal[t], binormal[t]};
SetOptions[ParametricPlot3D, Mesh -> None, PlotPoints -> 30, 
  Boxed -> False, Axes -> False, ViewPoint -> {-2.37, -0.52, -2.35}];
i = ParametricPlot3D[solid /. {h -> 1}, {t, 0, 8}, {s, -Pi, Pi}, 
   PlotStyle -> Cyan];
j = ParametricPlot3D[solid /. {h -> -1}, {t, 0, 8}, {s, -Pi, Pi}, 
   PlotStyle -> Purple];
u = ParametricPlot3D[solid /. {t -> 0}, {s, -Pi, Pi}, {h, -1, 1}, 
   PlotStyle -> Yellow];
v = ParametricPlot3D[solid /. {t -> 8}, {s, -Pi, Pi}, {h, -1, 1}, 
   PlotStyle -> Yellow];
p = ParametricPlot3D[solid /. {s -> -Pi}, {t, 0, 8}, {h, -1, 1}, 
   PlotStyle -> Blue];
q = ParametricPlot3D[solid /. {s -> Pi}, {t, 0, 8}, {h, -1, 1}, 
   PlotStyle -> Blue];
Show[i, j, u, v, p, q]