:wasalamex
:ma:, I certainly agree this is a good da'wah opportunity.
7 minutes is indeed very short, so you have to be very precise in what to include. It won't be possible to go into detailed explanations, so the idea is to deliver a simple yet key message, an introduction to Islam, that will :ia: cause people to want to know more. I don't think it will be possible to go into misconceptions unless there is time for Q&A, in which case you will need to prepare the answers!
I think topics that must be included are: the concept of God/Tawheed, the Prophet Muhammad :saws: (and can include mention of Prophets in general), and the Qur'an. There should also be a summary of the purpose of life. Something like the first post here:
http://www.islamicboard.com/discover...tart-here.html
You can browse websites which provide concise information like the leaflet posted earlier, to give you more ideas of how to deliver the information.
If there is time, then maybe there could be a page listing and addressing some of the top misconceptions? It will need more thought depending on the time available after you have put together the main part.