Can you provide a link? This should not happen as the heaidng is set to a maximum width of 73%. You can check within main.css, and you should have this :
article h2 {
line-height: 1.5;
margin: 25px 0 10px;
max-width: 73%;
position: relative;
z-index: 101;
}
If your theme version doesn’t have it the same, just replace. max-width is what interests you in the first place.