Parenting a teen is difficult for myriad reasons.  As they develop and grow through adolescence, they will continually test your boundaries, and question many of your parental decisions. (Especially your best decisions.)

For instance, you’ll ask them to return home at 9:00p.m., (because you want them to arrive safely), and they will object and explain how every other parent lets their child stay out until 11:00p.m. (they want to socialize).  You will ask them to study (you want them to succeed academically), and they ask you to wait until they're off the phone or computer (they want to do well in school, but would rather have fun in the moment).

When these situations arise it is perfectly natural to doubt your parenting.  To ask yourself: Am I providing the right boundaries? Am I too strict?
Not strict enough? Should I compromise?

Beneath the surface, you ask yourself the more important questions:

How can I keep them safe?  How can I support them in school? In life?

Finally, underneath all of these questions is your unconditional love, and overall concern for their well being.

Parenting Actions
Trust yourself, and when you make a decision stick with it. Do not waiver, and do not bend. Teens succeed when they have clear and fair boundaries.