Please help me when I am in the act of committing a sin and I tell myself stop Allah is watching the Shaytan tells me 'so what if allah is watching" and I continue doing the sin. What should I do.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Remembering that his Lord is watching is one of the greatest means of repelling the slave from sins and acts of disobedience, as Allah Says (what means): {But as for he who feared the position of (i.e., before) his Lord and prevented the soul from [unlawful] inclination. Then indeed, Paradise will be [his] refuge.} [Quran 79:40-41]

Therefore, if you remember when you are committing a sin that Allah is watching you and seeing you, and knows what you are doing, then this is a Mercy from Allah Who provided you with this deterrence so that you would stop the sin. Hence, you must stop immediately from committing that sin and not act as if Allah is the least One you care to see you (whilst sinning). If you are ashamed that people see you committing that sin, then Allah is more deserving to be bashful from than people.

Therefore, do not respond to the call of the devil who incites you to do evil with constant incitement. Rather, you must strive to repel him and repel your own evil self, and seek the Help of Allah and stop immediately. Indeed, Allah guaranteed to help those who struggle against their own self for the Sake of Allah; Allah Says (what means): {And those who strive for Us - We will surely guide them to Our ways.} [Quran 69:69]

Allah knows best.