Is it possible to waive off the negative effect on defaulting by a few days by mistake?

To avoid such a situation in the future, set a date in which you'll make all your credit card bill payments along with your utility bills. Choose 1 or 2 days before the first bill payment in any calendar month. For example, if the first bill payment is on the 5th of every month, then you can set 3rd as the day of all your bill payments. This way, you won't forget the due dates of payments and can avoid late charges.
For this one, don't worry much. Most of the times, the CC companies won't update it to the bureaus since you've made the payments but it's always better to notify the cc company.

Call your creditor immediately and inform him about it. It's only a few days. So, it won't matter much. Have you crossed the grace period already? Request the creditor to not report it to the credit bureaus.

You should inform your creditor about is as soon as possible. Explain the reason behind the default. Request your creditor not to report it to the bureaus. If your past payment record is good, you can get a positive answer from your creditor.

Call your creditor immediately and inform him about it. Explain the reason asap and ask them to not report it to the credit bureaus.