You might get lucky heading toward the back and find two seats together. However, let's do the math...
According to Seat Guru, SW planes have between 21-24 rows of 6 seats ( 24 * 6 = 144, 21 * 6 = 126). Even assuming no one in business class, no preboards, and no family boarding, you have 100 people boarding before you (A16-60, B1-55). Add in preboards, family boarding, and business class, and you could have an additional 10-20 people on board before you. If it's on one of the smaller planes (with 21 rows), you'll probably get middle seats. If one of the larger, you might be OK.