Breast lump grown twice in size

Hi everyone,

I'm really new to this forum, I was on here last year after discovering a worrying breast lump. I initially didn't think much of it as I was told that I was young (26) and it was just a small lump, however, the panic set in when I was sent for a biopsy. 

I was lucky that everything seemed to come back clear, and the lump was diagnosed as a Fibroadenoma and I hadn't thought much about it following this.

I don't really know when it happened, but I discovered a few weeks ago that the lump had seemed to have grown nearly twice in size. I immediately contacted my GP who didn't seem too concerned and thought it would be fine (due to my age etc) she said she would contact the breast clinic but 'it was likely they'll say just to leave it'. 

I've now gotten another appointment to go back to the breast clinic for tests and I'm unbelievably anxious. Is it common for these to grow so quickly? Is it possible to be misdiagnosed? 

For context it grew from a pea size to a grape, maybe 2/3cm. 

Does anyone have a similar experience? Thank you.