Newbie problems; gradual build up of distortion as I add tracks

Welcome to the forum.
When mixing, it's a good idea to have all your audio tracks sent to a Master bus, then that bus output to the sound card/interface. That's so you can control the summed audio and lower the volume of the Master bus if it's distorting.
How are you routing your tracks?

Thanks for that; okay, I'm using an old version, 4.0.1 of Sonar and I havent been on the forum for ages as I did a lot of stuff in the studio over the last few years.  I actually dont like tech stuff I'm very impatient, but I know thats a bit of a Luddite attitude! So I really dont know what a master bus is! I looked in the help section but its as clear as mud. I am really looking just for a decent enough demo nothing stunning.

Thanks guys, very helpful, and its much better now I've tried those things. Here is the result!

I don't think you can post a link until you have something like 25 posts.
 
Anyway, depending on what template you start off with, if starting off with none, you may not have a Master  Bus, a normal template will make one. In my version (7) I still can not find how to add a master bus, other buses are fine.
But then  if you have a Master Bus, the output of each track goes to the Master Bus, and the Master Bus goes to the output of your audio/interface that you are using to playback the audio.
 
But if you do not have a Master Bus to begin with, all that needs to be done, is adjust the volume of each track down until the total mix (listening to it) is out of the red on the ouput meters probably up on top (the two meters - left and right there) which is how it is in my version.
 
You may have recorded each track fine and not in the red, but totally it is like what was said - cumulative so adjust the volume on each track down a certain amount until the total mix is out of the red.
 
Computers are not analog and usually over a 100% wrecks the recording. I suppose there is much better equipment in the respect if you pay thousands of dollars for it, but for home recording that is not going to be so, and going into the red overdrives the computer chips and thus the wrecking of the recording.
 

Spacealf 
Just insert a stereo buss and name it MASTER, that's it. Point it's outputs to your interfaces main outputs. That's all a master buss is. Right click and you can assign it as the default for all new tracks. 
 
Because a lot of my songs sometimes start life as one of my old MIDI files, they open with absolutely nothing going on. SO I had to figure out some quick ways to flesh them out into a working project with all the bells and whistles. 

I don't think you have told us which interface you are using. Does it have a software mixer? 

You still didn;t tell us? 

Just listened to your song. Very nice. It has an Al Stewart quality to it.
SoUnds like you are getting a handle on the overall levels problem.
How are you recording your vocals, and that lovely "whale cry" guitar?
I'm guessing single mic to a stereo track.
Don't do that. It gives you 1/2 of a stereo track, and pins the sound to the left side.
Record to a mono track. ie, select Left Input-Mono. This will bring your vocals to the center, where they belong, and allow you to move them within the stereo field.
You can salvage these tracks by splitting them into mono tracks. Delete the right side track, as it contains no data.
Play with panning on the remaining track, and you will hear the freedom of movement you now have.
 

Thanks Bob et al.
I use a Samson G Trak condenser mike with a usb. In fact that is how I came to use Sonar as it was bundled with the box! As for guitar sound I used my trusty Marshall and a Les Paul. I got the echo sound by copying the guitar track and just delaying the copy a bit. (  One of my guitar heroes is Brian May and I find some of the things I do tend to sound a little like that, ie delays and one or two parts fitting together in a sort of harmony.)