Consider using mx-auto in your code. Here is an example that should help you:
<html>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<link href="https://cdn.jsdelivr.net/npm/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="47252828333433352637077269766974">[email protected]</a>/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3" crossorigin="anonymous">
<script src="https://cdn.jsdelivr.net/npm/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="dbb9b4b4afa8afa9baab9beef5eaf5e8">[email protected]</a>/dist/js/bootstrap.bundle.min.js" integrity="sha384-ka7Sk0Gln4gmtz2MlQnikT1wXgYsOg+OMhuP+IlRH9sENBO0LRn5q+8nbTov4+1p" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/@popperjs/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="21424e534461130f10110f13">[email protected]</a>/dist/umd/popper.min.js" integrity="sha384-7+zCNj/IqJ95wo16oMtfsKbZ9ccEh31eOz1HGyDuCQ6wgnyJNSYdrPa03rtR1zdB" crossorigin="anonymous"></script>
<script src="https://cdn.jsdelivr.net/npm/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="ccaea3a3b8bfb8beadbc8cf9e2fde2ff">[email protected]</a>/dist/js/bootstrap.min.js" integrity="sha384-QJHtvGhmr9XOIpI6YVutG+2QOK9T+ZnN4kzFN1RtK3zEFEIsxhlmWl5/YESvpZ13" ></script>
<div class="row ">
<nav class="navbar navbar-expand-lg navbar-light bg-light">
<img src="/resources/images/Babyboom_logo_main.png" width="200" height="50" alt="BabyBoom logo" class="navbar-brand">
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="col-md-9 ">
<div class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="col-md-3 navbar-nav mx-auto">
<li class="nav-item">
<a class="nav-link" href="#">Sessions</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Contact</a>
</li>
</ul>
</div>
</div>
<div class="col-md-2">
<a class="btn btn-primary float-right" href="#" role="button">Book Now</a>
</div>
</div>
</nav>
<!-- end snippet -->
</html>