I often have heard my japanese colleagues a double て used. example, kuruma nottete, ushiro mitete, genba ittete.
what i know is single te is command but what does double te mean? does it make more stress or what?
yoroshiku onegai itashimasu
The second て form is the て form of the verb that is used after the first one which is いる in this case.
見てて → 見ていて
As for the meaning, there is a slight nuance but if you know the difference between the る and ている form, there should be no problem. It would be like saying in English:
後ろ見て : I looked back (and...)
後ろ見てて : I was looking back (and...)