I looked at your last 3 losses in 10 minute games...
In game 1 you could have captured a bishop for free but did not.
In game 2 you missed a knight capture on f7 by your opponent which you could have prevented.
In game 3 you gave your opponent a free pawn by not defending it, then later sacrificed a piece for not a lot.
Its not so much the opening, but doing the basics well. This means if you can take material for nothing, you have to see it and do it. If your pieces are threatened you must take steps to prevent losing material - make the opponent work hard to gain an advantage, don't just let them have it. If you can do this consistantly you will quickly move into the 1000+ rating range by beating players who can't.
In terms of opening play though I will say in the 2 games i looked at where you had white, both went 1.e4 e5 2.Nf3 Nc6 3.Be2... 3.Be2 is a super passive move which asks no questions of black. 3.Bc4 or 3.Bb5 are much more to the point. Try to put your pieces on their most active squares.
I'm noticing that when I play live games and against computer above level 5 that when I try to follow my opening plan (play the center, develop, castle) my opponents often attack my pieces right away and then I spend the rest of the game in defense mode responding to constant attacks while my minor pieces often end up getting stuck on the home rank. Any tips?