Hello Jamil,
Since that is the case, please send us a screenshot or an example url like from a demo sites so we can have an idea of what might have occurred and how you can resolve them.
1.) Assuming the gaps is coming from the section, you may need to set the top and bottom padding of the sections to 0.
2.) The font sizes were dependent global settings in Pro > Theme Options > Typography > Body and Content and in Pro > Theme Options > Typography > Headers.
3.) The single product page is designed to have the product image on the left and the product details on the right.
4.) You may edit the product content for the description tab in Pro editor. It must be enabled first in Pro > Theme Options > WooCommerce > Single Product > Product Tabs
5.) The cart and checkout pages were generated by the woocommerce shortcode as shown here:
Hope this helps.