StrlEIT, I forgot to answer your last sentence.
I don't have any reason to believe that you have deficiencies, based on having multiple design classes already. Obviously more design classes are always a good thing, so I'd jump all over them if they're offered.
In general, a lot of structural guys are weak at dynamics, so have trouble understanding floor vibrations, EQ stuff beyond equivalent lateral forces, and wind beyond rigid bldgs. I know I sure fell into this category. If you don't have it already, you should try to get a super strong background in structural dynamics and vibrations. If your university offers a vibe class, usually in the ESM or ME dept, that would be good. If there's an EQ-specific class, that would be great too. I'd prefer both if possible, even though there's some overlap. Those subjects are hard enough to warrant some of it twice. The ESM and ME versions get into things that the CE EQ classes don't.
If you don't have it already, you should try to get a very strong background in matrix structural analysis and, secondarily, finite element analysis that's specific to structures. Don't get bogged down in porous media and other stuff not relevant to your work.
If you're not planning a thesis option, I'd recommend some technical writing also. If you're like most of us, you're a so-so writer after undergrad. More practice at that can never hurt. Aside from reports and memos, you might get involved in committee work at some point and need to develop text, examples, etc.
Same goes for public speaking. You might want to give seminars or presentations over the years. I can think of some very famous and noteworthy SEs out there who could use some work in these areas, LOL!
Anyway, these are the types of things I'd be thinking about.
FWIW, two of my friends, both PEs at this point, did their MS part time while working. It worked out great!