After binarizing the image you can use the function bwmorph() to make a bridge between the white lines present in the image.
After bridging if you like you can use the function imdilate() to enhance the connected line. You can tweak various parameters of the function to get your desired output.
close all; clc;
a = imread('2.png');
a = imbinarize(a); % Binarize the image
b = bwmorph(a, 'bridge'); % Use this to connect the pixels
se = strel('line', 20, 180); % Structuring element for dilation
b = imdilate(b, se); % Dilating the image
imshow(b);
See if this is your expected result.
