what is the normal clutch for a budgie mine has seven eggs and in not sure if she is finnished, she laid the seventh today

usually anywhere from 4-8. Some have more, some less. Sometimes the first one or the last one aren't fertile (or any in between) so hopefully you get left with about 5.

In a couple of days if there are no more then she is finished. Hens usually lay every second day

so far only 3 of the eggs are fertile.

If you know that only 3 are fertile then you don't have to worry about over crowding the box or over working the parents. The Pie gave great info about the average clutch size. Your hen may continue to lay more if the first few are infertile.