I've done a total of 4 BIAB batches and each time I learn more. My first batches gravity was way off like yours. It also is a brown that I am drinking now. It is still pretty good even though I made mistakes. My last batch was last weekend, a porter that was to come in at 1.062. I hit 1.058 so I am much closer. Didn't calculate my boil off correctly and had about 3/4 gallon too much so that might have been the difference.
The few things I have learned are this.
1 - I have the LBS double crush my grain, or I use a blender to get it very fine.
2 - Controlling your mash temp is key (as someone already stated) and it can get away from you very easily.
3 - I suspend my grain bag above brew pot using a string and pulley system to let much of the water drain from it. I use a small pot lid to lightly press the grain to get a little more water out.
Utilizing all my grain by making sure it was crushed really good and controlling my mash temps were the things I noticed that made the most difference. I still have a lot to learn but feel more confident that I'm getting a handle on it.
Don't lightly squeeze that bag, try to crush it. You're trying to get sticky wort out of there. Any you leave in reduces your efficiency. When you are done the grain should look pretty dry.:rockin: