Your education provider provides each student with the same number of Studiosity interactions, to ensure fair and equal access to the service. Unfortunately these limits are set at a university level and can't be extended on a student-by-student basis.
You'll see your allocation on the left hand side when logged in to your Studiosity account homepage:
If you would like more support, please speak to the student services and/or student union at your institution, to let them know. It's important they receive this feedback from students, and they may be able to point you in the direction of another service available to you.