Gutenberg are stored in the post content. I think this is not useful but did you tried to edit this in your template? If the Gutenberg block is already in a class of container like this you can add a full width and style it with CSS after.
<div class="container">
<div class="full-width guternberg-block">
My Block
</div>
</div>
style {
.container {
// this is a example
width: 1200px;
}
.full-width {
width: 100vw;
position: relative;
left: 50%;
right: 50%;
margin-left: -50vw;
margin-right: -50vw;
}
}
you can read more here https://css-tricks.com/full-width-containers-limited-width-parents/
