Hi, A psa of 3 isn't high and could be said to be well within the range of normal at 62. Although the average is quite a bit lower from what I've read.
I had the biopsy first 3 years ago, got the result in 2 weeks and had an MRI and Bone Scan 4 days later. Now having an MRI first is regarded best practise.
My biopsy was 12 pin and only 1 pin found bad cells even though only one side of my prostate was hard, so they'd know roughly where to look. I don't know what would have happened it they'd missed it. In your case it seems they think something is there so likely they'd give you a template biopsy.
As the psa is 3 there is a good chance it's early and prostate cancer is usually classed as slow growing. If the biopsy finds something it could be better to have it before the MRI although if it doesn't and they think it needs another biopsy then it probably isn't.
It must be tough to decide whether to ask for an MRI first. I must admit I just wanted quick treatment and might have been fortunate it went reasonably well.