BFP! But...

Samantha • Just had first baby Oct. 22, now trying to avoid getting pregnant!
I just got m first ever BFP! But I'm worried, because I only peed on it for about 3 seconds, and it showed positive about 3 second after I put the cap on. Could it be invalid, or does that just mean my hcg is high? If I really am pregnant, I'm about 5 weeks.