since you = sinchu correct? [closed]

It's not wrong, although it might be considered a bit informal.

The pronunciation of "since" in isolation is generally transcribed as /sɪns/. However, this pronunciation may be affected by the phonetic process of epenthesis. This causes /ns/ to change to [nts], or /nʃ/ to change to [ntʃ] (or more generally, this process may cause any nasal consonant to extrude a plosive after it when it is followed by a voiceless fricative in the same syllable). So many people pronounce "since" the same as a hypothetical word "sints"; that is, [sɪnts]. This occurs due to the articulatory difficulty of producing a nasal consonant directly followed by a voiceless fricative. John Wells describes this process in the following blog post: some day my prints will come.

The pronunciation of "you" in isolation is generally transcribed as /juː/ (stressed or "strong" form) or /jə/ (unstressed or "weak" form"). However, the pronunciation of the two words /sɪns/ and /juː/ in sequence may be affected by the phonetic process of assimilation. The assimilation is the change of the sequence /sj/ to [ʃ], more or less. (More precisely, the change to [ʃ] is assimilation, and the loss of one of the segments is called "coalescence"). The /s/ is said to be "palatalized" in this environment. Assimilation of /s/ to a following /j/, resulting in [ʃ], is not mandatory across word boundaries, but it is common. John Wells describes this on a page from his old phonetic blog (scroll down to the Thursday 15 January 2009 post "Asshimilation").

When you combine these processes, you get "since you" pronounced as [sɪntʃuː] or [sɪntʃə], with a "ch" sound (IPA [tʃ]).