First of all, welcome!
You will need to extend the project length. The default length is 1800 frames (30 seconds @ 60 fps).
To increase the project length, open the Project settings (Ctrl + Shift +P).
Under the Time Unit heading, there is a setting for End Frame (the first frame is designated with "0", so the default 1799 gives you 1800 frames).
For 3 minutes (180 seconds), you would set the end frame to 10799 (for 10800 total frames).
What is often confusing for new users is the difference between the internal frame rate that iClone uses (default is 60 fps) and the framerate of the rendered video, which can be something different (I use 30 fps). In iClone 8, you can now make the internal frame rate the same is the desired rendered frame rate. That way, if there are 900 frames on the timeline there will also be 900 frames in the rendered output.