Should I worry that my bachelor's degree will be revoked because I only completed half my internship hours? This happened in 2016. In my college where I got my bachellor degree (no thesis required), one of the requirements to get that degree is to have 600 trainee hours at a company. The company send a letter to the college which states that I only worked for 300 hours as a trainee (which is correct).

However, Now I've just remembered that the college considerated the 300 hours as 600 hours. Should I worry that they will find out their mistake and revoke my bachelor degree?

I remember that I told the secretary that they were making a mistake but she didnt care and told me to go away.
You shouldn't worry about it. The general principal is that the dean of the college that signed your diploma felt you had met the requirements. It would be unusual to second guess that decision years after the fact without a compelling reason (like new evidence of fraud). 

We've had a lot of questions about degree revocation recently. Everyone agrees that this is extremely rare, and almost non-existent when the student acted in good faith and the university deliberately issued the degree. It is difficult to imagine a mechanism where the university would even notice the discrepancy, much less care enough to pursue the matter. 

By the way, I recently gave the opposite advice to a similar question. But the situations are a little different--in the other case, there was a question about whether the degree had been awarded, and why it was awarded. Your degree was issued according to the normal process.