Opinions please

I'm 7.3 weeks pregnant with my twins, I bought a scale to keep track of my weight gain. Before I got pregnant I weighed 125 jumped on the scale today it said I weigh 140. How did I gain that much in a matter of few weeks? Should I buy a new scale or could this scale be correct. I'm concerned because during my last two pregnancies the most I weighed was 150 and that was close to delivering them.