It is doable. Many of my sisters, including myself,have jobs, hold positions, have internships and have classes and do fine. I suggest being a server, its the most money you can earn in the least amount of time. I have found that Greek life has kept me sane over the years. Its my happy place
Being in a sorority teaches you excellent time management skills that you will need later in life. Also, if you ever find yourself slipping, you would have at least 50-100 girls by your side waiting to catch you.
I say since youre a JR that you go for it and see what happens. You might regret it if you dont, and by that time you would be a senior and the chances at receiving bids that late in the game is rough, no matter what school your at. And even if you did receive a bid that late, you would only have a year with your sorority before you graduate. Good luck with your decision!