I have a question, if one performs ghusl of janabah and makes the intention to wash his body in parts for example, first he makes the intention to wash his head face and neck, then when washed, continues to make the intention to wash the right side of the body. If he does this and completes his ghusl and when finished doubts whether he made the *intention* to wash his *left* side AFTER completing his ghusl, is he required to perform it again despite washing his left side completely as well?

I find myself a doubtful person anyway so I don’t know if that’s relevant?

The intention for ghusl is for the entire act and it is sufficient that it is unspoken. Regardless, you should disregard your doubt if you are kathir al-Shak