How to manage css to html colomn out of paper

I have print pdf using dompdf and i use basic html but , i have a problem on paper on right side , my colomn is out of paper like this picture or on this link image . this image showed colomn and this left is correctly but on this right its out of range . i need to create like this left side but i dont know.

its my code :

CSS

    <style>
* {
  box-sizing: border-box;
}

/* Create two equal columns that floats next to each other */
.columnA {
  float: left;
  width: 68.7%;
  padding: 10px;
  height: 200px; /* Should be removed. Only for demonstration */
  border: 1px solid black;
}

.columnB {
  float: left;
  width: 68.7%;
  padding: 10px;
  height: 120px; /* Should be removed. Only for demonstration */
  border: 1px solid black;
}

.columnC {
  float: left;
  width: 33.3%;
  padding: 10px;
  height: 200px; /* Should be removed. Only for demonstration */
  border: 1px solid black;
}


/* Clear floats after the columns */
.row:after {
  content: "";
  display: table;
  clear: both;
}
</style>

Colomn

<div class="row">
  <div class="columnA" style="background-color:white;">
    <h2>Column 1</h2>
    <p>Some text..</p>
  </div>
  <div class="columnA" style="background-color:white;">
    <h2>Column 2</h2>
    <p>Some text..</p>
  </div>
</div>
<div class="row">
  <div class="columnB" style="background-color:white;">
    <h2>Column 1</h2>
    <p>Some text..</p>
  </div>
  <div class="columnB" style="background-color:white;">
    <h2>Column 2</h2>
    <p>Some text..</p>
  </div>
 
</div>
<div class="row">
  <div class="columnC" style="background-color:white;">
    <h2>Column 1</h2>
    <p>Some text..</p>
  </div>
  <div class="columnC" style="background-color:white;">
    <h2>Column 2</h2>
    <p>Some text..</p>
  </div>
  <div class="columnC" style="background-color:white;">
    <h2>Column 2</h2>
    <p>Some text..</p>
  </div>
 
</div>

i try this change this css float its make change the posisition but i can do correctly , if i change this float 50% its will create space on this right correctly but i dont need 50% my case is 68,7%, can someone help ?