That's a lot better, though I think you may need to adjust the pixel height and width settings in the option box to represent the proportions of the rectangle you drew on the map a bit, since you shouldn't really be able to see any of the edges of the rectangle you used to demark the chosen area.

Now then. Down to the thin coastline issue...

You could just make the line thicker by using the change properties tool, but if you have any really sharp angles on that coastline anywhere at all it may create undesirable artefacts in the form of spurs that go shooting off into the distance at a tangent to the actual line. And because the tracing is so fine I would say there is a very high chance of that being the case.

Try it and see what happens, and if it doesn't work give me a shout. There is another much more complicated way of sorting this out.

I think I should add here that taking short cuts by not reading the manual and learning how to use the software before you started on this project is causing you an awful lot of unnecessary hard work, and that it might have been quicker to do things the other way around. It certainly isn't all that easy for me, either, since every time I make a suggestion I have to remember that you aren't going to necessarily understand what I'm going on about