Gallery still in one column

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

body {
  font-family: 'Poiret One', sans-serif;
}

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

a {
  text-decoration:none;
}

img {
  max-width: 100%;
}



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

h1 {
  font-family: 'Alegreya Sans', 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;
}
/* green header */
header {
  background: #6ab47b;
  border-color: #599a68;
}
/*nav bg on mobile devices*/
nav {
  background: #599a68;
}

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

/* links */
a {
  color: #6ab47b;
}
/* nav links */
nav a, nav a:visited {
  color: #fff;
}
/* selected nav links*/
nav a.selected, nav a:hover {
  color: #32673f;
}