Hi,
with the Studio release, you have plenty of solutions to merge several photos. Just some ones :
- Retouch tool /Magic eraser : apply it on the "ugly lines"
- draw a selection of 20 pixels width on the ugly lines and right click / Antialiasing / Progressive contour,
and menu Filter/ Visual effect / Gaussian blur
- don't use Past special : increase the canvas size of the first image. Paste the second image which becomes a Layer
Draw a selection on the border which will cover up the first image, and menu Layer/ Transparency / Transparency gradient
- Look at the tutorials for an Artistic assemblage, at this page :
http://photofiltre.free.fr/tutorials_en.htm