A pretty design, and I like the way you attached the star. I see you hooped the card - you should not, you'll never get rid of the indentations. A nice stabiliser also helps prevent tearing along the stitches, you could even use cotton instead of stabiliser. Afterwards you cut it out 1/2 " or so from the stitching and stick a piece of paper or card the over the back. The thickness of the card is of minor importance as long as it's not too thick.
I normally use 80gr card but I only hoop the stabiliser and use a bit of spray glue to keep the card in place.
It stitched out really nice. The thickness of the card stock was probably fine you just don't hoop it. You hoop sticky back or plain stabilizer and a bit of glue and stitch the card stock to that.