Let's take some scenarios here:
Scenario 1. The launch attracts a lot of subscribers and your infrastructure can't stand up to it or holes in your application are found.
Okay this is a pretty good problem to have - people want your product, nice. But the experience hasn't been A+, not nice. Guess what? People are (for the whole part) understanding and logical. They understand that software matures over time and, as an early adopter, they accept that they may have to put up with a bug or two. Software breaks, get it over it.
Scenario 2. You've thrown a party and no one shows up (aka few subcribers). Okay this sucks from a business POV but on the plus side you'll be able to pay your few early adopters some extra attention and find out why they chose your product. Use this information to improve your marketing.
Scenario 3. Middle of the road - an average number of subscribers, with some bugs discovered. This is a good sustainable start, keep it up (and crush those bugs you know about).
Regardless of what happens, things will be fine. Don't sweat it :)