My question is that I performed ghusl, but a few hours later I spotted a small peice of something under my nail, I did not know of this while performing ghusl, and I feel like that tuing under my nail stopped water from going there. and I and doubting whether I should do ghusl again, or if it is valid.
Salam, I believe this may be overlooked as you did not see it during ghusl. These may also be the thoughts of waswas so it is best to avoid these doubts.
This link may be better suited for your question so I think it would be better to read this rather than listening to anything else beforehand, I hope I have helped.