Hi i measured 8mm at 7+3 u/s, placenta in the way of rump, strong hr... is this measurement too small? had strong rising hcg no bleeding and symptoms

Small yes but: This is small for a crown-rump measurement at this gestational age (the rule of thumb is the crown-rump length+6.5= menstrual age in weeks +/- 3-5 days) but if as you say the placenta was in the way of getting a good view of the rump and all else is well, then a repeat ultrasound later is likely to give a better measurement. Hope this helps.