Portfolio not floating to 2 columns

/**************
GENERAL
****************/

body{
  font-family: 'Open Sans', sans-serif;
}


#wrapper {
  max-width: 940px;
  margin: 0 auto;
  padding: 0 5%;
}

a {
 text-decoration: none; 
}

img {
  height: auto;
  width: 100%;
}




/****************
HEADING
****************/




#logo {
  text-align: center;
  margin: 0;
}

h1 {
  font-family: 'Ubuntu', sans-serif;
  margin: 15px 0;
  font-size: 1.75em;
  font-weight: normal;
  line-height: 0.8em;
}

h2 {
  font-size: 0.75em;
  margin: -5px 0 0;
  font-weight: normal;
}

/****************
NAVIGATION
****************/

nav {
  text-align:center;
  padding: 10px 0;
  margin: 20px 0 0;
}




/****************
FOOTER
****************/

footer{
  font-size: 0.75em;
  text-align: center;
  padding-top: 50px;
  color: #ccc;
}

/****************
PAGE: PORTFOLIO
****************/


#gallery {
   margin: 0;
   padding: 0;
   list-style: none;
}

#gallery li {
   float: left;
   width: 45%;
   margin: 2.5%;
   background-color: #f5f5f5;
   color: #bdc3c7;
}



/******************
COLORS
******************/



/* site body */
body {
  background-color: #fff;
  color: #999;
}

/* Blue header */
header{
  background: #101074;
  border-color: #00407f; 
}

/* nav background on mobile */
nav {
 background: #00407f;
}

/* logo text */
h1, h2 {
  color: #fff;
}  

/* links */ 
a {
  color: #000000;
}    

/* nav link */

nav a, nav a:visited {
    color: #fff;
}
/* selected nav link */
nav a.selected, nav a:hover {
  color: #fff;
}