When it comes to financing your studies there are several options to consider:
There are many scholarships available which are not awarded due to a lack of applicants. It is defiantly worth having a look.
Institutes are always looking for (affordable) employees. Advanced students are welcome assistants in lab internships or in research. HIWI jobs are often very flexible and usually require little working time.
Many companies offer working student positions. Usually better paid than HIWI-jobs they are often less flexible and harder to obtain.
If you require urgent financial support the Studierendenwerk will lend lend you up to 1500€ free of interest.
Other options: For further possibilities head to money and of course you can look for work outside of the University.