/oʊ/ dipthong is the one heard in most American pronunciations of the GOAT lexical set, so also in words like no, toe, tone, so, sew, boat, soap, tow, soul, sold, roll, cold, folk, polka.
In some speakers, the
/ʊ/ rounding may be less noticeable in non-terminals like soap than in terminals like sew.
See here for a very basic treatment.
See here for a rather more elaborate one.
At first I was confused by your
/oʊvərˈsiz/, and so thought that the IPA you were looking for is
[ˈoʊvɚˌsaɪz]. It might have been clearer to me personally, and more quickly, if you had written
[ˌoʊvɚˈsiːz], but you did nothing wrong.