After creating MX and TXT records (at your DNS provider), you can use online DNS query tools such as Google Admin Toolbox: Dig to check if you have configured the DNS records properly.
To check the two MX records, go to Google Admin Toolbox: Dig: MX, and type in your domain. If they have been set up properly and propagated, you should see the values as shown in the screenshot bellow.
To check the two TXT records, go to Google Admin Toolbox: Dig: TXT, and type in your domain. If they have been set up properly and propagated, you should see the values as shown in the screenshot bellow.
Note: It may take a minute or as long as several hours for DNS changes to propagate ("show up") in the online DNS query tools.