I work part time for a church 20 hours a week.
Even though it is a church they want to run everything like a business.
I have no problem signing in and out for work but sometimes after a long day I forget to sign out that day, so the next day i would write my time in.
That was before they started getting more strict with the signing in and out.
Now if you don't write your time in they put a highlite thru the days you don't work or write your time and won't pay you for it.
They won't give you a warning that they are going to not pay you.
Is this legal and if not what do I do?

You must be paid for all hours you work. However, the easiest way to solve this is not to forget to sign in/out.