Looks like you were hogging wood out a little too aggressively with that planer! Planer should never take off more than about 1/16" at a pass, and preferably less. Not the best way to thin a board down from 2.5" to 1.5" wide!!
I used a hand held saber saw to cut a 1x3 plank in half to make two bows. Worked just fine by going slow and sticking to the line.
You could actually use a hand saw to cut the board in half lengthwise.
Hand saws have been around a lot longer than electric ones.
You'll need a couple good clamps to hold the board in place and a good table of some sort to clamp to; but you'll need those things anyway.
Depends on how far into the 1-1/2" section you've gone. No reason your bow can't be 1-1/4" wide just as well; it's not like the God of Bows will smite you for being a little narrow.
Your other choice would seem be to go back to the lumberyard and get a real 1x2 (3/4 x 1-1/2" actual) and start with that...
