Wa'alaikummussalam sis, takyah risau sangat lah but this is something best checked dengan your doctor atau midwife sebab they can actually feel and examine to make sure everything's okay, especially since you're mentioning the hardening of the belly too. A few of us mums went through similar things at 29 weeks and it turned out to be Braxton Hicks contractions mixed with baby movements, but better safe than sorry kan, especially for first pregnancy. Go see your gynae, they'll put your mind at ease dalam masa 5 minit je. Take care, mama!