Ay normal lang yan, mama! At 30 weeks, 8kg gain is actually on track, doctors usually say 10-12.5kg total is ideal for normal BMI, so you're doing great pa lang, hindi ka nag-oovershoot yet. I have a few mum friends din na nag-gain around that same pace and they all had healthy babies, so honestly, as long as baby is measuring well and your OB is not worried (which she's not!), you can breathe easy, just stick to what she said about controlling your diet at staying active if you can. If it'll help your peace of mind, ask your OB at your next visit kung ano exactly ang target weight gain para sa'yo by due date, pero from what you've shared, sounds like you're doing just fine!