Hcg not doubling every 48 hours?

Hey! So Im not sure how far along I am as my cycles are irregular. But I went in to get the pregnancy confirmed at the doctors, and they checked my beta levels and they were quite low at 140. So they had me come back in 48 hours to get tested again, and they were at 211, that was yesterday. Today they had me come in again, (less than 24 hours later) and they are at 321.

They want me in next week to get tested again and hopefully an ultrasound if they are high enough. Do these levels seem like they’re alright? Based off experience maybe? Just really nervous and I’m looking for some success stories from people who were or are in a similar boat as me!!