Hello heli
You almost got it. You will need to keep the sidebar and the sections in two columns but you added only one as col-md-3 for side bar, also they need to be inside a row. doing this might change the look of your home page and also might disturb the styles of it as far as the responsiveness is concerned it might get disturbed too. but if you really wanna do it then please check the code below we did some changes in your given code you will get the idea.

get_header();
<div class=”row”>
<div class=”col-md-9″>
// echo ‘dfajsdlfjlajsdlfjla’;
$lz_fitness_home_sections = lz_fitness_home_section();
// print_r($lz_fitness_home_sections);
foreach ($lz_fitness_home_sections as $lz_fitness_home_section) {
// echo ‘lz_fitness_home_section-> ‘. $lz_fitness_home_section;
get_template_part( ‘template-parts/section’, $lz_fitness_home_section );
}

?>
</div>
<div class=”col-md-3″>
<?php get_sidebar(); ?>
</div>
</div>
<div class=”clearfix”></div>

<?php get_footer(); ?>

Thank you