What should I learn next? (trying to land my first job in the industry)

Your current skillset is terrific, and if you add nothing to it prior to applying for jobs, you'll probably be fine.

If you can learn Camtasia and a little more about video editing that's always good, and I also encourage learning more about audio editing. The nice thing about audio editing is that you can download Audacity for free and it doesn't hog your system resources like video editing can. https://www.audacityteam.org/

Storyline does offer some minimal audio editing which is handy to make a quick fix, but if you want to do anything more robust you'll need something like Audacity or Adobe Audition. 

The Association for Talent Development, td.org, offers some certifications if you think those would help you. I did fine for many years without any certifications, but sometimes companies like to see them. They can be expensive, though.

Learning Captivate is not a bad idea if you can manage to download a trial version. I've never liked Adobe's user interfaces on any of their programs, but they are a big company and companies tend to want to stick with one suite of tools. See where you can get with a trial version and then let people know that you have used it, are less expert than other tools, but with your tech skills you will be an expert quickly. 

Finally, I'm not sure where in the world you're located but when you do start applying for jobs consider that many companies and Federal agencies in the US often don't like to hire eLearning designers as a regular position. Try to find some contracting agencies. They are often hiring, and will hire people for full-time, regular positions with benefits. Then you may be assigned to different companies as needed. Often you can work from home. :)

Good luck!