Hi Alex,

I may not be even 1200 ! I just want to try to give advices which
could help you in some way.

The first game

20. Rc3
You have probably forgotten the Black bishop on g7 at that time. 20.
R3d2 would have been better.
This is quite a blunder, which self explains why you cannot win over
such higher rated opponents.

The last one :

After 19. ... Bxf3, you didn't see the mate in two, so this is what's
wrong.

I think you should try to focus on basic principles, and leave
openings variations for the moment.

Don't get frustrated. And try to play against players of your level.

Regards.