I have never had one before and at enrollment, decided to open one up

I elected to put in $300 which they take out a portion out of each paycheck from Sept. through May (I work for a school). When I log into my account it shows available $300 to use. My last day at the school is Friday so my benefits will be done. So my question is, do I only have available the amount that actually has been taken out from my paychecks or the full $300? I don’t want to lose money but I also don’t want to use the money and have to pay it back.