In my opinion you should use it yourself...as people here would not be interested for this deal, I've seen Starbucks cards much lower than 50% on several marketplaces, most of them are carded/use of illegal tricks...but these days no one cares, they go for the cheapest option...
If you've bought it with your own money, then it might not be the best place to sell, also you are a newbie (me tooo..

), so you are basically wasting your time and energy... may be you can try giftcard marketplace, sell the card, then buy BTC for $10 in any btc market, coinbase..etc...its not a big deal...