A quick glance suggests a missing divide command in the "parameters = " expression on the last line.

See attached. Refraction_Demo_Doc_version.mw

Note, this document was constructed as part of my experiment with Maple Cloud. 

As someone who spends time trying to get students to use Maple to solve physics / engineering problems because I would rather have them work on those problems, and not math problems, I can understand your frustrations. There are many times I find Maple coding to be less than "math intuitive."

However, for this situation, let me say, what are you trying to do ? Are you trying to take the derivative of f(x) with respect to x and then set the x in the outcome to be equal to 3? This outcome would be 3.  Or, are you trying to take the derivative of f(x) after you have put in the value of 3 for x? Because that is how I initialy read it. (Think arcsin(sin(x)). Pass x to sine, do the calculations, then do the arcsin of the resulting calculation.) For this reading, the outcome is 0. 

Since I'm going to assume the former, then what one needs to know, when Maple sees g(x), x is a variable. However, when Maple see f'(x), it sees the " ' " as the derivative with respect to the variable x.  So for me, the most readable and understandable way to write these statements is:

It performs the calculation of the derivative before it evaluates the outcome using x1 as the value for x. 

Download Derivative_example.mw

Based on my experience with updating numerous copies of Maple, to update within a shorter period of time, I recommend going directly to the Maplesoft website and downloading the update: https://www.maplesoft.com/support/downloads/m2018_2update.aspx

Yes, odd. Correct statement appears to be evalb(true) as in: 
 

if evalb(true) then .... end if;

I too use the right-click button as an instructional tool. In working with this option, I've never seen a menu not show up. However, I've had two situations occur: 1) the first time the menus are loaded, there can be a delay. On some computers, it can be noticable. 2) sometimes one can click on a phrase, either the input or output, and there is nothing for which it can do to it. 

From a pedagogical perspective, I teach the students to write some simple code. For me, nearly all of the math problems can be performed upon learning about 10 commands. But I use the right click for maybe that calculate that requires at most a couple clicks. For a different pedagogical perspective, Robert Lopez should weigh in here. 

I don't quite understand why you want to adjust the size. Regardless, I don't believe such an option exists.

However, I do feel having an option within a right-click menu option would be very useful to those of us who both display plots of a worksheet and print those worksheets. In the former situation, a larger plot is useful, in the later situation, a smaller plot is useful. This might mean establishing a set of sizes: small(100 x 100), medium (200 x 200), large (400 x 400), and default (what was established under plots:-setoptions). 

For inserting equations, plots, etc. from Maple into a Google Doc, I use a screen shot application. In Windows, this is the "Snipping Tool". For me, it works well enough for most situations. 

As an physics instructor who has seen this problems for decades, may I suggest the following: given the symmetry and anti-symmetry of the wavefunction, select initial conditions at x=0 where the system flips from symmetric to antisymmetric, i.e., psi(0)=1, D(psi)(0)=0, etc. This will lead you to more accurate values for the energy of these levels, that is: try different values for E, the value of the energy until your odeplot produces that which are seeking. Using this method to shoot around (often called the “shooting method”), you will obtain a more accurate value for E in whatever units you are using.  I suggest Marko Horbatsch’s book: Quantum Mechanics using Maple.  http://www.maplesoft.com/books/details.aspx?id=214