On Full Tilt PT3 can figure out your finishes in tournaments because FTP writes summaries to your computer. For other sites you need to import tournament summaries or manually enter the information, see the
Tournaments FAQ.
With regards to your cash game graph: if you look on your Sessions tab for yourself you should be able to find the session that's causing the problem. If you then click Database --> Database Management --> Purge ... you can remove just that session from your database.
You can link your new username to your old one or the other way around whichever you prefer. You do this by going to whichever name you want to be your main name on the Texas Holdem -> General tab, then click the blue Edit link under the word "Aliases" (it's near the top right of the General tab), then add your other name to the name you're on as an alias. Note that the more hands you have on the player you're adding as an alias the longer the process will take. (So it's faster to add a new user with 2 hands to an old user with 200,000 hands than the other way around.) Either way once you do this all stats from both names will be merged.