If you're talking about adding it to a video project -- there's no way to make it automatically loop. You need to just place it several times, end to end, on your Soundtrack audio track.
The way that you are doing it is the only real way. Unlike an Audio editor that uses loopology, and Clips designed for this, Video has a set Duration.
Now, especially if the file is not muxed, i.e. Audio & Video in one file, you can Select the first instnce of the Clip and Ctrl-c (Copy), then, use the End key, if you have no other Clips in the Timeline, and hit Ctrl-v (Paste). If you have other Clips, you can use the PageDn (or PageUP) key to step one Clip at a time. Be aware that the PageUp & PageDn keys will go the Head, or Tail of any Clip in the Timeline, so be careful that you have reached the end of the Clip that your trying to extend. Hit Ctrl-v, at each Clips Tail to Paste another instance of it. The reason that I mention muxed Clips is that often, Pr (I've seen this in PrPro, but have never done it in PE) will cause the Audio to go "flatline." Whle this can be fixed, I use caution with Copy/Paste and muxed Clips.
You could do another Project, where you just to the above, but with an otherwise clean Timeline. Then Export that Project as a DV-AVI (or appropriate HD file), and Import into your regular Project. Same work, but with a clean Timeline, so End-Paste, End-Paste is a simple thing.
PS you might explore Time Stretch, if you do not have to increase the Duration too much.