Typically the heartbeat will slow as the baby grows. From what I understand this is normal. My peanut started at 179 8 weeks, now 17 weeks we are around 155.
Congratulations you may just have an active baby on your hands!
It's fine. Baby was probably really busy during or just before the u/s. No worries, the heartbeat rises and slows depending on baby being awake or asleep.
It's not too uncommon, but it is a little fast. If it was really low, then I would worry.