Although I think it's great for a first edit, I might have a few tips that I believe can be helpful for future edits:
1) In general, I choose either one audio, music OR river audio. So I would probably turn down the audio of the raw clip and leave us to listening to the music MOST of the time. There are exceptions though, like perhaps when giving a yell or when something from the live audio is worth listening too.
2) I prefer short, clean transitions most of the time. In your video, there are jump cuts. Basically it goes from one clip directly to the next. In iMovie, I prefer "Cross Dissolve," "Fade To Black," and "Cross Blur." Drag the transition of your choice between each clip. You can edit the transition length, and usually a half second works great..
3) Leif posted something about GoPro tips on his blog once, and it's EXCELLENT. GoPro footage turns out way better in sunshine. I also prefer using mine in a variety of ways. Wearing it on my helmet facing downstream is probably my least desirable method. It's great perspective to film other kayakers, but because of the wide angle, it's best to be uncomfortably close to other paddlers.
4) I usually start and end my videos with a blank black screen.
5) I do my best to transition from clip to clip with the music. For example, when we hit the chorus in many songs, that's a great way to transition to the more exciting exciting clips.
6) I have found that my videos have gotten generally shorter. I have gotten pickier with using my footage, so what used to be a several minute video has turned into much shorter as I've gained experience. This helps to keep viewers watching.
7) I am NO video expert, but I think you might find examples of what I'm trying to describe on my youtube channel. Check out MicahK1982's channel - YouTube
for some of my videos. Good examples of what I'm trying to describe can be found in a few of the kayaking videos, like "Winter kayaking on the North Fork." Check page 2 if you are wanting to see more of my videos.
I think your first edit wasn't bad, so keep up the good work.
I use iMovie and think it works great. What program are you using?