I got the Marvel card a couple of weeks ago. After the approval, I continued with the app process and created an online account....like you I had not idea my SL. I logged onto the account to find a disappointing SL of $1000. A week or so later I received my card. The card paperwork said my SL was $3000. Hmmmmm....I logged back into the online account and it said $1000. I activated the card over the phone and moments later I logged back into the online account and it said my SL was $3000. Go figure??? LOL
Congratulations on the Synchrony MARVEL card and please don't sweat the start limit right now.
Use it, pay it, rinse and repeat and before long they will pleasantly surprise you with a much higher limit. Just keep your TransUnion FICO Score going up anyway you can. They follow that like a hawk and will reward you for it's improvement too.