Yes, this was not a good idea. Readers don't get a notification when you make a new comic series, thus they never saw you created chapter 2. Also more often than not people don't like to sub to a new comic at all - the library can fit like 500-1000 comics and many people have it filled to the brim.
I don't think you can merge two series either, sorry (although you can look closely on dashboard, but I don't think it's an option). Well, things happen, it'll be alright. I would post whatever pages of chapter 2 you already posted in chapter 1 (just not all of them at once! give yourself more chances to be seen) and make an announcement or two...or a few on chapter 2 and send readers over to the first one - use banners, links, whatever you can.
Don't spread your comic and your readership thin until you know the content is really different from the main plot so creation of the new page is justified.