Suzabelle
if you know are definately going on those dates and using SWA, you do not suffer any penalty if you find the prices have gone down later, you can change to the lower fare
usually, when you do that, they will give you a "refund" of some sort ( some here have gotten credit to their "credit card" )
but , if it is ticketless travel funds, it usually expires one year from the date of your "original" reservation being booked
you might also look at fares on different dates around your original travel dates to see if lower fares might be there ( not always viable if your dates are inflexible though )
hope things work out for you