@Dammyyou have 3 options
1) buy a data addon 1gb for $30
2) top up account and do an early renewal can take up to 48 hours for mods to reply.
3) do an immediate plan change to a plan with more data
options 2 and 3 require you to basicly forfit the remianing time of your current plan. (ie restart a new plan cycle), butthese are usually more cost effective $/gb vs the data addon
Other options include renewing your plan earlier, but you will need to contact moderator (expect 1-2 days wait) or change plan immediately to another data plan. You will lose remaining allottment of your original plan. No pro-rated plans with Public mobile.