Not really - remember that it is never correct to write the pronoun 'I' with a lower case letter (i). You should always use a capital letter 'I'. Apart from that mistake, your sentence is fine. You can use either the past simple ( 'I just realized') or the present perfect ( 'I've just realized'). The meaning is the same. Is it true? Do you really hold everything upside down? Or only some things?

yes it's correct, but it's better to say I have just, instead of I just