<Note>Mary, your boyfriend's mother just called. She told me to inform you to pack up. Their family is
going to Cancun this weekend and want you to join them on the cruise trip! Lucky you.
Don't you plan to use the weekend to study for the exam on Monday?
If you can't make it, remember your roomie here is available this weekend!

Are there any mistakes?

Three actual error:

The use of family as a singular subject for is but a plural for want. I would use wants.

Saying cruise trip isn't at all natural. Just say cruise.

Didn't you plan, not Don't you plan.

Now, is it natural?

Do people go on a cruise for a weekend? I don't know. Cancun seems pretty remote for a weekend.

"She told me to inform you" - far too formal for someone you call a "roomie." "She told me to tell you to pack up." Better "She said you should get packed!
Students: We have free audio pronunciation exercises.
Thanks, GG. I agree with all your points. It's difficult to construct sentences
that sound natural when you don't have 'instinct' that a native speaker have to guide
you. For example, I consciously know inform is too formal for a casual conversation but because
I'm so used to using it, it slips into casual conversation unnoticedly.

By the way, should error be used as an uncountable in the following?

You wrote: three actual error
No, that was MY error. The first time through, I saw only the verb agreement, and then I went to rewrite it and forgot to change it to errors.