WordPress isn’t adding anything that’s messing with it. The problem is that on Ontraport you placed it at the very top in a full-width div. On your WordPress site you placed it in the content area, which is not full width. So the left edge of where it appears is not on the edge of the screen. You’ve made it position: fixed, and aligned it to the top with top: 0 (or the bottom, it’s different on the site compared to the code you’ve pasted here), but you haven’t aligned it to the left with left: 0;. Add it and it will appear in the proper place:
<div id = "countdown_timer" style="position:fixed; width: 100%; left: 0; bottom:0; z-index:1000;" ><script type="text/javascript" src="https://timerz.xyz/timer/egc.php" data-launch_owner_email_hashed="94bd214b329301668349352de430bb6d" data-launch_id="204" ></script></div>