Hi I Am 26 Yrs And I Am 29 Weeks

Hi I am 26 yrs and I am 29 weeks pregnant this is my third pregnancy first both deliveries were c- section n both was healthy. Yesterday in usg it is anterior placenta with second grade maturity before in 22 weeks usg it was grade 1 but now it is grade 2 maturity is any problem with this .Now I am 78 kgs doc is saying it is over weight and u have to reduce now otherwise it will be problem for ur baby I am very much tensed about this please say me about this and yesterday she has given me some betnesol injection for the safety of the baby n today also one dose is there why this injection is any problem for the baby please requesting you to answer my questions thanku