What are you expecting, what are your goals? Paid or free app? Who signed up for the list. Are they targeted? What % of them do you think will download? Do you have other ways to get people to download your app instead of the waiting list? What are you doing to build a relationship with the list to entice them to download. Is the app any good? Is it exciting? Does it solve a new problem? Do you need a wait list at all?
As a quick answer I suggest forget about the wait list and make your app awesome! Then drive people to download the app, not join the list.
Build a list once you have the app, to remind people how great/useful it is with helpful articles etc. So they keep using it.
P.S. the percentages you mention are meaningless on such small numbers. Forget about % growth until you have a few 1000 in the list.