It is highly reassuring but not conclusive. Need to repeat the test after 3 months of the exposure. It is almost unlikely for the 8 week test to turn otherwise in the next 4-5 weeks, (as none of us has seen so), the test is only considered conclusive after 3 months as per CDC guidelines
Since the nurse told you the official, Swedish guidelines regarding rapid HIV-tests stipulates that there should elapse at least eight weeks after risk for an HIV negative result to be totally accurate, you can accept your negative results as conclusive. You tested at 53 days which is only 3 days short of the 8 week guideline. The results will not change in 3 days. Even if you wait to retests at 12 weeks, as diver58 has said, none of us has seen 8 week negative results change at 12 weeks.. I believe you only need to retest at 12 weeks for YOUR peace of mind.
The most common test in the US is the 4th generation DUO which is conclusive at 28 days post exposure. 3rd generation window is 12 weeks, but I see countries that state 6-8 weeks is considered reliable. I sincerely believe the best thing you can do is follow the guidelines of the HIV Specialist you are working with. Hopefully we will soon have international guidelines.
Without doing some research, I couldn't name them off the top of my head. YOU could research them