Dentist confusion

I went to a new dentist because my old dentist wasn’t taking my insurance anymore. So this new dentist tells me I need gum treatment and that my insurance doesn’t cover it so they said either I pay upfront or I can apply for a credit card, see how much I get approved and pay in payments. I took that route and got approved for so much money. Well I did not know that I already have to pay it.

I went back to my original dentist because they ended up taking my insurance after all and the doctor didn’t notice anything wrong with my gums. So now idk what to do. Am I able to stop the credit card I applied for or do I have to pay since I got approved and already shows when I need to make the first payment? Or am I able to cancel it?