Dates are wrong surely!!!

So according to a <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">pregnancy app</a> my LMP was 5th jan making me 4wks pregnant but my HCG blood level was 48 and apparently 3.5 weeks pregnant. Having cramps and slight light brown discharge...I'm a mess and can't stop crying incase my second bloods on Wednesday show a problem :(