Hello, and welcome.
I'm so sorry that you lost that first little kitten. : (
The oxytocin brings on contractions, but sometimes there are several hours between kittens. If she was mated by more than one male at different times during her estrus cycle, the kittens could be days apart. The cat's uterus contains two 'horns' and not all kittens are ready to be born at the same time, in some cases.
Are you still at the vet or did they give her the shot of oxytocin and send you home?
The exam given by the vet should have been able to tell if there are remaining kittens who are still alive.
Here is additional information about feline pregnancy, labor and delivery:
I understand your financial bind at this time, but she may need a C section if she's not progressing normally with a vaginal delivery and/or if any of the kittens or your mom-cat is in any distress. Try applying for Care Credit to enable you to pay for a C section, if necessary, or ask your vet if you can pay out the remainder of the fee in installments. If you've been going to this vet for a while, they might agree. Here is information on Care Credit:
I hope all will be well with your cat and her litter and please let me know how things are going. Thanks!