How to cut a one piece sheet of vinyl, for a perfect fit. But, I would still try and get the molding off. Make a paper pattern(building paper is best, but thin cardboard works). Tape the "T" shape well. You don't have to have it tight to corners/edges, but around an 1"space is OK. Cut triangles out of paper all around the edges. Smooth out, then cover triangle cuts with good tape & some thin on the edges(to hold pattern PUT from bunching up, as you crawl around). Take a builders framing SQ is best, but any ruler type thing with a metal edge to run your cutting knife against. You lay metal edge tight to wall all around the whole edge, & marking your line on the INSIDE of SQ/ruler. Pull the pattern slowly up. Place on it sheet goods per the pattern lining up. Push the tape back down in triangles(might have add some new & thin piece down edges) if got too dirty & not sticking well. Now you lay your SQ/ruler down with the backside lined on your marked line like it was. The metal edge is now AT the same place as your wall was. Make your cut, moving the Sq/ruler along. If using framing SQ, make sure you are using the SAME side 1 1/2" vs 2", as you were when marking.