For example Sid's second-ish meeting with Roshni was him sitting on top of her car waiting for her. Exactly like Raghu who waits on top of her car, waiting for him to settle the extra money Roshni gave her.
He himself talked about him only taking money/asking for money that he spent/deserved. which again Raghu did.
When Roshni got angry that Sid didn't listen to her pleas that she didn't put mangoes in the milkshake, and Sid realises his mistake in accusing her, he goes to her place to apologize to her. When he gets out of the present box, after Roshni yelled at him, the first song he sings in front of the door(before anyone opens it) is that "Agne mein...baba" song(I'm sorry, Hindi isn't my first language so I dont understand the lyrics). He again sings this song as Raghu in the elevator scene.
Sid was scared of rats (and maybe cockroaches too, I haven't seen all the episodes), and when there was a rat in the room, his reaction was the same with Roshni as Raghu's was with the cockroach.
There were alot more smaller similarities I noticed as well. Like some similar one liners Sid said. Like him being the mahan/smart person who said this thing, or about his respect for women.
Like I understand we're supposed to get hints that Raghu is Sid. But wouldnt the similarites make Roshni question him being Sid even more?