Thank you for reaching out to us through the Community. You can make your newsletter longer by adding more blocks to it. The more blocks you add from the Build tab in the editor, the longer the email newsletter will become. To add a block in, you can either drag and drop the block in the newsletter or double-click on the block and it will populate to the bottom of your newsletter. For a tutorial on our drag and drop feature, please click here.
Also, as a general rule of thumb, you want to make sure you don't have to scroll more than three times on your mouse when viewing the email campaign. The reason is because longer email campaigns usually do not produce good open rates or click rates. The principle is: less is more when it comes to email newsletters. For more information on improving your open rates, click here. For click rates, please click here. I hope this information helps! Let us know if you have any further questions!