Multipule Attribute prices

Hi im using shop responsive theme 8.1, and under attributes i have 4 sections,
so heres what happens

main theme price lets say £1.00
attribute lets say small, im adding code [0.30] this works fine and adds the total to £1.30 but if i add a 3rd attribute lets say large [0.60] it will then add this price to the total but will not add the previous 30p to the total as well can this be fixed ?

Dave