Sabar sabar dulu! Ada jugak baby yang slow in reaching milestones but perfectly fine, setiap baby ada timeline sendiri apa. Tapi since she's almost 6 months, definitely worth checking with your pediatrician just to be sure everything's on track, maybe they'll give you some exercises or tips to help strengthen her neck and core untuk duduk dan meniarap. A few of my mum friends went through the same worry, and most of the time doc just reassured them or gave simple things to do at home like tummy time. Don't stress too much, first time motherhood can make us worry about everything, but better safe than sorry kan!