I found the problem! the config is good but i was accessing to https://myapp.com but in my vhost config i did not have ssl (:443) config, so obviously doesn't work. But if i go on http://myapp.com work's fine! little mistake... 
Thank you for the help!
I share my /opt/bitnami/apps/myapp/conf/httpd-vhosts.conf for anyone who need it, Just follow the previous steps by tomasp and works fine 
<VirtualHost *:80>
ServerName myapp.com
ServerAlias www.myapp.com
ProxyRequests Off
ProxyPreserveHost On
ProxyPass / http://localhost:3000/
ProxyPassReverse / http://localhost:3000/
# redirect www and non-www http routes to https-non-www:
RewriteEngine On
RewriteCond %{HTTPS} off [OR]
RewriteCond %{HTTP_HOST} ^www\. [NC]
RewriteCond %{HTTP_HOST} ^(?:www\.)?(.+)$ [NC]
RewriteRule ^ https://%1%{REQUEST_URI} [L,NE,R=301]
</VirtualHost>
<VirtualHost *:443>
ServerName myapp.com
ServerAlias www.myapp.com
ProxyRequests Off
ProxyPreserveHost On
ProxyPass / http://localhost:3000/
ProxyPassReverse / http://localhost:3000/
#redirect https-wwww to https-non-www
RewriteEngine On
RewriteCond %{HTTP_HOST} ^www\. [NC]
RewriteCond %{HTTP_HOST} ^(?:www\.)?(.+)$ [NC]
RewriteRule ^ https://%1%{REQUEST_URI} [L,NE,R=301]
</VirtualHost>
