Bad grades can only hurt you if you do not know how to work around them.
There are a lot of jobs out there that could care less about your GPA once you get some experience.
One of the best things that a college student with a science or engineering major can do is to take as many classes as they can for credit/no credit. Earning the equivalent of a "C" will not hurt you because you can still get credit for the class. No grade is recorded on your transcript, only the credit for the class.
If you messed up in classes, try to retake them to get a higher grade. The new grade will replace the old grade. The old grade will still be visible on your transcript, but the newer grade will be calculated and the old grade will not count. That will boost your GPA more than doing great in newer classes.
One other thing that I recomment for science students is to get some work experience. Getting an internship is definitely worth it. Even if you have to spend an extra year in school, do it. That job experience will come in handy once you start interviewing. By working in the industry, your lab skills will improve and you will know more about how a lab works than 90% of other students and 50% of faculty/professors.
The main thing to do is to be confident. If you let something like a number (GPA) get you down, you will probably have a very hard time being successful in life. There are millions of dumb people with confidence and people skills that outearn scientists simply because they are tenacious and never quit.
Do not be passive. Be agressive but respectful. If your GPA is low, get an internship, do an undergrad thesis and emphasize those attributes. Leave out yor GPA unless it is asked for.