You can't see your actual MMR, just what OP.GG tells you "it might be".
Since we don't know each and every thing that gets to be calculated in the math for MMR, you can never know for sure. The algorithms OP.GG uses are different from what Riot has.
So basically, even if OP.GG tells you that "you are where you deserve", Riot's actual data may think otherwise. Last season, before Fortuna released in Warframe, I was winning 22-24 LP per game while losing 16-18, but OP.GG was telling me my MMR was lower than my rank, but if that'd be true, then it should've been the opposite, losing 22-24 and winning 16-18.