I recently converted to PRE20 from PRE12. In PRE12, I could create an 8.6 GB folder, then use Imgburn to create DL DVD's.
In PRE20, I created an 8.6 DL ISO file. Then attempted to burn the DL DVD with the same version of Imgburn. Imgburn displays the following message (attached MS Word file) and will not burn the DL DVD. (BTW - I am disappointed that Adobe has removed the ability to burn directly to DVD and Blu-Ray in PRE20.)
How long is your movie? As a rule, it's a good idea to avoid burning a dual-layer home-burned disc if possible. For one thing, it's frought with challenges, no matter which software you use. For another -- the attention span of a viewer watching even well-edited home movies is between 20 and 40 minutes.
Finally, I'm not clear what you're seeing when you say ImgBurn created an ISO file when you attempted to burn your ISO. Is that what you're saying?