Reliability of tests

Ja

I had a positive test yesterday but am really worried that it's not accurate and I'm getting my hopes up. Was due on 3 days ago and took a test yesterday even though I felt like I was going to come on my period. I haven't (yet) and haven't had any bleeding but I'm just worried it is too good to be true. I had a chemical pregnancy in August and was really upset when I came on. Should I be excited or nervous? Do you think I should retest? Thanks!