I've masterbated at night and I can't do gusl now as I'm scared of my parents. can i do tayammum. Because I want to attain Farz namaz in mosque. I don't wanna miss it.
The only valid reason for a sane person to perform tayyamum is the absence of water. Which must be concluded after extensive search. This usually applies only for travelling people who are in a desert and even those must search for water before performing tayammum. As Allah the Almighty says:
And if you are ill or on a journey or one of you comes from the place of relieving himself or you have contacted women and find no water, then seek clean earth and wipe over your faces and your hands [with it]. Indeed, Allah is ever Pardoning and Forgiving. (4:43)
So you can't pray unless you've performed ghusl.
No, fear of parents is not a valid reason for tayammum.
Just keeping it to the point, though there are other things worth talking about here.