It seems that no one is exactly sure what you want to do, since the super obvious plot(x,y,'b-') doesn't seem to be it.
So I'll throw out a couple of guesses.
To close the figure (if that's what you want) you can tack the first point onto the array:
xp = [x, x(1)];
yp = [y, y(1)];
plot(xp, yp, 'b.-', 'LineWidth', 2, 'MarkerSize', 18);
grid on;
To make a bunch of points in between, you'd have to use polyfit and polyval() for each segment. Here it is for one segment with endpoints (x1, y1) and (x2, y2):
numNewPoints = 100; % Whatever you want.
newx = linspace(x1, x2, numNewPoints);
y = linspace(y1, y2, numNewPoints);
coefficients = polyfit([x1,x2], [y1, y2], 1);
newY = polyval(coefficients, newx);
