Plan b question really worried please help?

It's all totally normal with Plan B. It's a huge dose of hormone (progestrin), that can give you lots of hormonal side effects, such as those you'd get if you were pregnant, ovulating or if you were on your period.
You may find that the spotting turns into bleeding, which can sometimes be heavy.
You may also find that your period is late. Sometimes it's only late by a week or two, but for some women, it can be a couple of months. Anything is possible with Plan B.
If your period doesn't come on time, you can do a pregnancy test, to put your mind at rest, & know for sure that it is just the Plan B.