mantel mount with only 2 studs available
You will be fine as long as your screws are long enough to bite into the studs. 43lbs isn't that much.
For peace in mind, I would put a third screw in the center. I would push a &quot;hollow wall anchor&quot; into the drywall.  There are many styles for different weight ratings. Even the plastic ones that look very brittle are surprisingly strong.
I use them for my closet shelves and had no issues. The boxes on my top shelf is definitely over 50lbs.