HCG just over 5 after FET

Me and my husband did a FET 8 days ago and we had our first blood work today. Doctor called to say the HCG is just 5.3 but they want me to be cautiously optimistic.. I’m sure it is a chemical and it is really hard to be optimistic.. everything was so good - embryo quality / lining and progesterone levels and this was my last frozen one too.. which means we have no choice.. did anyone have HCG level increase after 8Days post FET?? Please advice I’m freaking out and depressed