Hey mama, congrats sa first baby! Usually ang ultrasound dating ay mas accurate kaya mas maaasahan mo yung June 24, lalo na kung done early in pregnancy yun (first trimester ang most reliable), kaya siguro yung center ay nag-compute based sa LMP mo lang. A few of us first-time moms namin, we trusted our OB's ultrasound more because nakita namin talaga ang baby, so go with June 24 as your guide pero of course baby pa rin ang mag-decide kung kailan talaga siya pupunta! Since malayo ang ospital, mas better na you're prepared earlier, mas relax ka pa, kaya go mo na rin makipag-consult sa OB mo about this, para clear lang lahat and you can plan your delivery day arrangements better. Good luck, mama!