I don't fault you for taking the 0% card. I do it all the time. For furniture, for tires, even for out of pocket dental bills and the vet a few times. It's the only time I will carry a card balance - when I am getting 0% interest. You've already applied for it and you have a year with no interest, I wouldn't pay it off early.
What I do fault you for is paying 2x for the same bed, buying the top mattress, and getting the warranty stuff!!! lol
When my son turned 14 last summer he was pretty much overdue for his own bedroom (had been bunking with his 11 year old brother). We converted the playroom back into a bedroom for him (my daughter was only 7 so she got shortchanged a play room by a few years, lol). He liked a bedroom set at Jerome's best (we are usually Mor people). The whole bedroom set was about $1900 including a full bed. I declined the $120 'bunky board' (instead found an $8 piece of plywood in Lowe's clearance section), declined the $300-500 in-store mattresses (ordered a highly rated mattress in a box from amazon for $165 and it's comfy!), passed on the in-store mattress protector and bought that at amazon too, and declined all extended warranties. I would have taken the 0% but, unlike Mor, it's one or the other - free delivery (it was actually $99 but I negotiated it to $0) or 0% and I needed the delivery (my car which can tow my trailer was down at the time). And I think I paid with my AOD for 3% CB. Lots of ways to save! 
I think many of us have done applied for a store card because of their promo (I know I have).
All is not lost though. Take advantage of the 0% and just pay it slowly throughout the 12 months. I would use your refund towards a different card that you carry a balance and are paying interest for (assuming you have one).
But this big question is..... was it the Synchrony card? If so, this may be a reason to close it off sooner rather than later even though it is a 0% deal based on how you feel about Sync!
The main fault is possibly getting a CC from Synchrony 
. The rest of the story looks fine.
You may not apply to any CC at the checkout of any store. It might be wisely to do your research and if the card matches your interest, apply online.
Fico8: EX~EQ~TU~840 (12 month goal~850).Since the damage is already done, enjoy the 0% APR period on the card. After paying it off completely, you may keep it as a SD card or close it to prevent any AA at a bad timining (one AA by a lender may tirgger the others to do the same).
@youngandcreditwrthy wrote:also @xenon3030 ask for a CLI every three months. Those Ashley's cards will go sky high to like 10 or 15k over night. I was pre approved for I think 8k around xmas this last year with only 660 FICOs
The Sync cards are not worth. They sometimes close the cards right upon using them. Now you are talking about CLI 
Giving generously CL to the people with very low Fico8 would raise also additional concerns on their quality of service, financial risk management, and their intention to do CLD in an unexpected future