m0ngr31 on "update_post_meta() adding extra things"

I'm trying to use the update_post_meta function to update a post when a button is pushed so that it will change something in the meta data for the post.

This is how I'm calling it:
update_post_meta($post_id, '_myrp_rating_categories', 'a:4:{i:0;s:1:"1";i:1;s:1:"2";i:2;s:1:"3";i:3;s:1:"4";}' );

But for some reason, the data ends up looking like this:
s:54:"a:4:{i:0;s:1:"1";i:1;s:1:"2";i:2;s:1:"3";i:3;s:1:"4";}";

Is there something I'm missing here?