Background Check - Made a couple mistakes

I made a couple mistakes in filling out the background check form.

1) I omitted the work info for a job I did for a month or two overseas while in the process of switching jobs. The job itself was 3 years ago and I never worked more than 4 hours a week. In the end, the employer didn't want to keep me on payroll and I was let go. I think I was paid under the table, and thus my salary probably was not reported to the local tax office. Would this show up on my background check? I honestly didn't consider this important enough to put on my work info section.

2) I omitted a couple temporary addresses, again purely because I forgot to list them.

3) I forgot that I had one B the last semester of high school, and just reported my HS GPA as 4.0. I think I am justified in listing it as 4.0 but not as 4.00 - the problem is I can't remember which I listed it as and I forgot to make a printout of this.

A lot of the above stems from carelessness rather than any malicious intent. I had a lot of things to worry about at the time, and I was not as careful as I should have been. I didn't realize my omissions after I had submitted everything already. To make matters worse, my firm has been mentioned many times already on this post as having a particularly demanding background checking process. How worried should I be?

Thanks.