craftgrrl | questions + blue necklace

I have been making myself a new bag, since my old one is falling apart, and I'm making it for the first time with a lining, now i have sewed the lining all up so its now a bag, and then i was about to sew the outer part and then sew them together, when all of the sudden i wondered, how much bigger should the outside be? I left about 3 cm room ( about an inch) on all sides for the outer side but im not sure if thats enough?

Also, I took a jar of mod podge with from the states and ever since I have been happily mod-podging various items, when I wondered, does that stuff yellow over time? because if it does, i might be better off not mod podging certain items xD

Unto the picture!
I made this necklace for my moms birthday, later I wrote unto the card with matching blue sparkly paint, happy birthday!
I got the rock at at some store where you could pick out stones and put them in a little bag, then I thought it would make a great necklace but this is the first time actually succesfully wirewrapping anything, usually I put like 10 meters of wire around something and it still manages to fall out xD
the polymer clay beads i tried to match as closely to the rock as possibly, they have tiny copper colored swirls together with some transparent swirls. the other beads are glass seed beads i still had. also sadly i made the fishing line to short, so that little end you see on the left top side was all i had to make a knot with, oops. i ended up making a knot using two tweezers and 20 mins of fidgeting x_X