Welcome. I'm a Christian here, too.
As you've learned, never alter a receipt -- for any reason.
I'm a little unsure if you shopped outside the allowable time or if the receipt time did not match the time you conducted the shop.
If it is the latter, you can simply confirm in your report that the times you've entered are correct and that the receipt time is off. I run into that frequently when I do gas audits. Generally, if it is only an hour or so off, I don't mention it. If it is off more than that, then I make note of it in the report.
If, instead, your problem was that you shopped the wrong hours, most people have probably made the same mistake. If you ever do that again, don't give up on the shop and, as you've realized, don't alter a receipt. Far better to submit the report and explain your mistake. There is one type of shop that company does that I know has a firm time window. I have been on the late end of that window by 5 to 10 minutes due to reasons beyond my control. I noted in my report and my reports were accepted. It really goes back to whether the client will accept it.
It's a painful lesson to learn, and you probably won't get rehired by them - at least not anytime soon. Let it go and move on. Tomorrow is a new day!
There is the truth.
Then there is the right thing to say.