Removing Sidebar Problems

Because there is 600px width content width with floating left. see in your style.css at line no. 358 following code

.content {
	float: left;
	width: 600px;
}

Change width to 100% it will center into all device

replace your .entry-title class at style.css(line no.502)

entry-title {
    font-size: 36px;
    word-wrap: break-word;
    line-height: 1.2;
    text-align: center;
}