I agree with all of the above answers. I have my own methods for all of them however. For a half-square triangle, the rule is add 7/8" to the finished size so for your 3" finished (3.5" unfinished), it would be 2 squares cut at 4 7/8" sewn a scant 1/4" from the diagonal and cut on the diagonal. I always go ahead & round up so I would cut my squares at 5" and then trim all my HST's after they are cut & pressed. You get 2 HST's from every pair of squares.
I do not like the jelly roll/tube method for HST's. There is way too much chance of stretching them out and fabric is too expensive to waste. I also don't like the magic square/blooming pineapple for the same reason.
I have tried reducing my stitch length at the end of seams but it just doesn't work for me. I guess I'm just too old school. A couple stitches forward/back then forward to start and back then forward to end has been working for me on any machine I've ever used for 40 years. My new machine even has a button that does just that so whomever engineered that nifty little feature must have learned the same way--LOL! I hate burying the ends so a true lock stitch is the only way for me when quilting. It's a lot harder to find those little knots and easier to ignore than thread tails and stitching coming loose.