Tawaaf without being in a state of purity is a topic concerning which there is a difference of opinion among the fuqaha'. The view of the majority of scholars is that tawaaf without wudoo' is invalid.
This has been discussed previously in the answer to question no. 34695
What happened in your case of uncertainty as to whether you were junub or not does not affect anything, because you are not certain that semen had come out. The basic principle concerning purity is that it is not rendered invalid unless there is something to prove that.
An-Nawawi (may Allah have mercy on him) said: If a person is certain that he was in a state of purity and is uncertain as to whether it has been rendered invalid, then he is still in a state of purity because certainty cannot be cancelled out by uncertainty.
End quote from al-Majmoo, 1/331
Shaykh Ibn Uthaymeen (may Allah have mercy on him) said: If a person is certain that he was in a state of purity, and is uncertain as to whether it has been rendered invalid, then he should proceed on the basis of certainty. This is general in application and has to do with the things that necessitate ghusl or wudoo'.
Then he gave an example and said: A man woke up and noticed some wetness on him, but he did not see an erotic dream and he is not sure whether it is maniy or not? He does not have to do ghusl when he is uncertain.
End quote from ash-Sharh al-Mumti, 1/190
Based on that, your tawaaf is valid and there is no blame on you for what you did.
For more information, please see question no. 83025.
Reproduced from Islam QA