Is there anyway to tell my gp1 class column to start at grid position 1 and end at position max - 1, bearing in mind this is a dynamic grid?
.widthContainer {
  width:400px;
  height:300px;
  background-color:#eee;
}
.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, 50px);
  grid-template-rows: repeat(auto-fit, 25px);
  min-height: 98%;
}
.grid>div {
  grid-column: 1/-1;
  grid-row: 1/-1;
  grid-template-columns: repeat(auto-fill, minmax(50px, 1fr));
  grid-template-rows: repeat(auto-fill, minmax(25px, 1fr));
  display: grid;
}
.gp1 {
  background-color: #aaa;
  grid-row-start: 2;
  grid-row-end: 4;
  grid-column-start:2;
  grid-column-end:4;
}
<div class="widthContainer">
  <div class="grid">
    <div class="bkg">
      <div class="gp1">
        <div>
          <p>content</p>
        </div>
      </div>
    </div>
  </div>
</div>