New to partial mashing

This is my second batch and I want to bump down to partial mashing because my brew pot, which was much smaller than I realized for a full wort boil, killed my target gravity. It was the only hiccup in an otherwise good brew day. But one question: Would it be acceptable to partial mash in my brew pot with a bag? The pot is six gallons. I'm only working with around 3lbs. of grain. I think it'd just be easier to do a smaller wort boil and then top it off with water in the fermentor. Any advice would help greatly!

yep. I only do mini mash biab & I think it's great.
I usually mash about 3 lbs of grain in a bag in 6 qts of water in my 5 gal granite ware canning pot.
meanwhile I heat 6 more quarts to 170ish in another pot for my dunk sparge.
add em together, stir in half my lme, heat to boiling, add hops & start timer.
after 60 mins, flame out, add remaining extract, cool to pitching temp, pour into fv & top off.
easier to do than to type...

thank you! that's reassuring.