You are doing a great job! It can be overwhelming getting breastfeeding off to a good start. The first few weeks are definitely the hardest.
First, consider contacting a lactation consultant or La Leche League leader. www.lalecheleague.org to find one close to you. A La Leche leader (free) could also recommend a lactation consultant. They can help get you on the right track.
Second, how is your baby's output? How much you pump and how formula baby will take are NOT good indications of how much breastmilk she's getting. If she gets nothing but breastmilk and pees and poops enough (6-8 good diapers a day), she's doing great and will gain weight. Formula supplements will tell your body to make less milk AND formula also takes longer to digest, making her space out her feedings more than she should at this age.
Third, nursing the baby frequently will help up your supply. You may also try eating oatmeal, some moms find it helps with supply. Also, lots of skin to skin time with baby and not nursing on a schedule, but at baby's indication (rooting, sucking fist, sticking tongue out) and at least 8-12 times in a 24 hour period. Do you hear swallowing sounds when she nurses? Is her jaw working? Do you leak milk and feel letdown? These are all good signs. Sometimes we feel like we don't have enough milk but we really do, it's just hard to tell how much baby is getting!
Fourth, nurisng in public is a new skill to learn. You can be more discreet than you would believe, but it takes practice and you can focus on that and get some tips once you get more comfortable nursing at home and make sure baby's getting enough.
You can do it! Support and information will help.