If i had unprotected sex 8 days ago and my period is almost 3days late will the pregnancy show up this soon on a blood test?

Possible: Although pregnancy tests are sesnsitive and realiable , during the first week of a pregnancy they can not pick up the pregnancy. You could try to check, but if the test is negative wait atleast a week then recheck.

Re do test: It takes the fetus about 3 weeks to make enough HCG for a positive pregnancy test. You may repeat the test at three weeks after sex, unless you get a period by then.