Hellllppp! It is never too early to think about retirement!

As many of you, I work for a private academy. My contract is permanent but I only teach 25 hours per week. The pay is not the issue. What IS the problem is the fact that Spanish Social Security (SSS)looks at my 25 hours/wk and considers that I am working part-time. What this means is, in terms years worked towards retirement (cotización), SSS gives me credit for only 6 of every 10 years worked(25/40= 60%). This means I (and anyone else in a similar situation) will have to work at the school for TWENTY FIVE (25) years to be eligible for retirement (25 years x .6 = 15 years). Do other people in this situation just go solely autonomo or maybe both SS and autonomo at the same time? Am I wrong? Thoughts?