That is normal.
Remember, your period may not come exactly 30 days from the last one... It can be more - like 31-35 days... Or less, like 25-28 days.
Especially in the beginning, it may not be regular or normal for a while.
If you are really concerned, ask your mom or a trusted adult. They'll be able yo explain it to you.
Don't worry. It is Normal for your period to be late. It just means that your period is irregular and it will become regular over time
its totally normal i get mine not regular and usually 18-19 days apart(ugh ik) but i just had my check up and told the doctor and she said that its normal for it to be iregular the first 2-3 years