Consider negative margin:
.container {
display: grid;
grid-template-columns: repeat(3, 1fr);
grid-template-rows: repeat(3, 1fr);
width: 500px;
height: 200px;
border: 1px solid;
}
.box {
grid-column: 2/3;
margin-left: -20px;
margin-right: -80px;
background: red;
}
.box-alt {
grid-column: 2/3;
grid-row:2;
background: blue;
}
<div class="container">
<div class="box"></div>
<div class="box-alt"></div>
</div>