Hi,
Open the style.css file and find there this code:

.bar-title {
float: left;
font-family: "HattoriHanzoLight", Calibri, sans-serif;
width: 620px;
position: relative;
z-index: 1;
}

change it to:

.bar-title {
float: left;
font-family: "HattoriHanzoLight", Calibri, sans-serif;
width: 510px;
position: relative;
z-index: 1;
}

Then find:

.bar-right {
width: 256px;
float: left;
}

and change it to:

.bar-right {
width: 365px;
float: left;
}

Then you can add another button shortcode without problems.

Let me know if you need more assistance.