Help start a NodeJs project after server restart?

I am new to Nginx and Ubuntu 16.04. I had an Nginx website up at armadasol.com with a NodeJS script. It uses a local MongoDB and PM2. I made some hard code changes on my home page and after I refreshed the website in the browser, the changes did not update. I restarted my server and now I get a 502 Bad Gateway error.

I have got the PM2 restarted. MongoDB is restarted

I use Nginx, NVM, NodeJs, MongoDB, PM2.

My nginx.conf server settings:

user www-data;
worker_processes auto;
pid /run/nginx.pid;

events {
	worker_connections 768;
	# multi_accept on;
}

http {

      server {
   listen         80 default_server;
   listen         [::]:80 default_server;
   server_name    localhost;
   root           /usr/share/nginx/html;
   location / {
       proxy_pass http://127.0.0.1:3000;
       proxy_http_version 1.1;
       proxy_set_header Upgrade $http_upgrade;
       proxy_set_header Connection 'upgrade';
       proxy_set_header Host $host;
       proxy_cache_bypass $http_upgrade;
   }
}

	##
	# Basic Settings
	##

	sendfile on;
	tcp_nopush on;
	tcp_nodelay on;
	keepalive_timeout 65;
	types_hash_max_size 2048;
	# server_tokens off;

	# server_names_hash_bucket_size 64;
	# server_name_in_redirect off;

	include /etc/nginx/mime.types;
	default_type application/octet-stream;

	##
	# SSL Settings
	##

	ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # Dropping SSLv3, ref: POODLE
	ssl_prefer_server_ciphers on;

	##
	# Logging Settings
	##

	access_log /var/log/nginx/access.log;
	error_log /var/log/nginx/error.log;

	##
	# Gzip Settings
	##

	gzip on;
	gzip_disable "msie6";

	# gzip_vary on;
	# gzip_proxied any;
	# gzip_comp_level 6;
	# gzip_buffers 16 8k;
	# gzip_http_version 1.1;
	# gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;

	##
	# Virtual Host Configs
	##

	include /etc/nginx/conf.d/*.conf;
	include /etc/nginx/sites-enabled/*;
}

Question 1) Why am I receiving a 502 error? Question 2) How do I prevent this next time I make changes in my files? Question 3) Is there a script anyone recommends that can restart my nodejs app when I make changes.