21 weeks pregnant normal thyroxine and high tsh. Dr rechecked waiting on results. How concerned should I be?

Wait for results. Normal thyroid hormone levels are absolutely essential to a healthy developing fetus and pregnancy. If you are significantly hypothyroid, your doctor will prescribe replacement thyroid hormone during your pregnancy. Total thyroxine is both bound and free thyroid hormone... The binding proteins (shbg) may increase in pregnancy so best to get repeat TSH with free T4 levels.
Somewhat. With normal thyroid, your baby is ok for now, and so are you. The high TSH suggests your thyroid gland isn't working as well as it should, which makes the pituitary gland make more TSH to tell the thyroid to work harder. Have a thyroid antibody test, a blood test, and if they are high, you may be on the way to hypothryoidism. Please have thyroid blood tests frequently to assess.