Hey @lea,
Please change the iframe width from 900 to 100% and apply this custom style. Add it to the Page Settings > Custom Code > Header area.
<style>
.css-1qw4ra5 {
width: 100%!important;
}
</style>
Keeping fingers crossed 
Hey @lea,
Please change the iframe width from 900 to 100% and apply this custom style. Add it to the Page Settings > Custom Code > Header area.
<style>
.css-1qw4ra5 {
width: 100%!important;
}
</style>
Keeping fingers crossed