Today she gave birth but we espexted 3 but then one came out and another one too but the second one didn't make it so I need help if its bad for a cat only give birth to one kittens.

Did you have her x-rayed before the birth to know how many kittens she would have?
Without x-ray or ultrasound there is really no way of knowing how many.
Cats typically do not have problems with birth, but problems are possible.
After labor has started the litter is usually complete in about 6-8 hours, however if mother is disturbed or becomes uncomfortable about something, ie: someone tries to mover her nesting area, someone bothering kittens etc. then she can halt labor for up to 24 hours.