Applying the tracks can be tricky, so here's how I do it.
1. First - check the fit of the drive sprocket onto the axle. If you are lucky this will be quite tight. Failing that - you could pad out the axle - or adopt a slightly different approach. But don't attach the sprocket.
2. Check the fit of the sprocket teeth into the track. If its bad, then shave off sprocket teeth as necessary. If this is good, then decide where the join should be, if there are side sponsons then the top of the track run, failing that - aim to have it directly under a wheel.
3. Pre-bend the track (gently) into a rough curve. Apply a small amount of superglue onto the sprocket, and attach the track to about a quarter of the sprocket. Pull taught - watching for curve in the track in the middle. Allow glue to harden.
4. Once set, push the sprocket onto the appropriate axle, don't glue.
5. Now run the bottom of the track along the road wheels to make sure the teeth are aligned and the road wheels straight and level. Adjust as necessary. apply a very small amount of Superglue to the rear of each wheel to fix the track into place along the bottom run.
6. Once set, gently rotate the sprocket to tighten the track between the sprocket and first road wheel. If the sprocket fit is tight, you don't need to glue the sprocket in place - otherwise a small dab of superglue to the rear of the sprocket to fix it in place.
7. Let everything set - it will look like this....
|Bottom of a Modelcollect T64
9. Bend to shape, and measure the join. DS tracks can be gently stretched, but generally speaking, they are normally a bit longer than you need. Cut as required and glue in final position.
Hope this is useful...