After some research and trial-and-error, I have managed to make this work as desired. I think the main thing that I missed was containing the table in a div.
Here is the Javacript syntax I used:
// Step 1. Connect JavaScript to the Storyline variables
var player = GetPlayer();
var RiseTitle=player.GetVar("varRiseTitle");
var QuestionText=player.GetVar("varQuestionText");
var TextEntry1=player.GetVar("TextEntry");
var TextEntry2=player.GetVar("TextEntry1");
var TextEntry3=player.GetVar("TextEntry2");
var TextEntry4=player.GetVar("TextEntry3");
var TextEntry5=player.GetVar("TextEntry4");
var TextEntry6=player.GetVar("TextEntry5");
var TextEntry7=player.GetVar("TextEntry6");
var TextEntry8=player.GetVar("TextEntry7");
var TextEntry9=player.GetVar("TextEntry8");
var TextEntry10=player.GetVar("TextEntry9");
var TextEntry11=player.GetVar("TextEntry10");
var TextEntry12=player.GetVar("TextEntry11");
// Step 2. The HTML Section - with the Storyline variables inserted
var contents = "<html><head></head><body style='width:650px;padding:20px;'>";
contents+="<div style='font-size:26px;font-weight:bold;margin-top:26px;margin-bottom:20px;'>"+RiseTitle+"</div>";
contents+="<div style='display:block;border-width:1px';><hr/></div>";
contents+="<div style='font-size:16px;font-weight:bold;'>"+QuestionText+"</div>";
contents+="<div>";
contents+="<table style='width: 100%' border='1'>";
contents+="<tr style='text-align: left;'>";
contents+="<th>CPU Model</th><th>Core™ i5-9400F</th><th>Celeron® N4020</th><th>Ryzen™ 5 3600</th><th>Athlon™ 3000G</th>";
contents+="</tr>";
contents+="<tr>";
contents+="<td>Clock Frequency (GHz)</td><td>"+TextEntry1+"</td><td>"+TextEntry2+"</td><td>"+TextEntry3+"</td><td>"+TextEntry4+"</td>";
contents+="</tr>";
contents+="<tr>";
contents+="<td>Cache Memory (MB)</td><td>"+TextEntry5+"</td><td>"+TextEntry6+"</td><td>"+TextEntry7+"</td><td>"+TextEntry8+"</td>";
contents+="</tr>";
contents+="<tr>";
contents+="<td>Price ($)</td><td>"+TextEntry9+"</td><td>"+TextEntry10+"</td><td>"+TextEntry11+"</td><td>"+TextEntry12+"</td>";
contents+="<tr>";
contents+="</table>";
contents+="</div>";
contents+="</body>";
contents+="</html>";
// Step 3. Open the document window, write the HTML contents, and open the print window
var myWindow = window.open("","Print","width=810,height=610,scrollbars=1,resizable=1");
myWindow.document.write(contents);
myWindow.print();
