You don't need to do string interpolation here, `<%= error %>` will get you there.

Also, totally optional, but you might consider outputting these errors as a list:

```erb
<% if @user.errors.any? %>
  <ul>
    <% @user.errors.full_messages.each do |error| %>
      <li><%= error %></li>
    <% end %>
  </ul>
<% end %>
```