Only a couple things I can think of will make it hit your arm aside from a low brace height. Sounds like your brace is probably about right for a longbow but on some recurves that would be low. Anyhow, if it's hitting in your forearm to elbow area instead of down by your wrist by where a watchband would be it's probably not brace height anyway.
Bow arm elbow position will do it if you shoot with a straight bow arm and your elbow pointed down. The guys talking about rotating your elbow or moving your grip are getting into this problem. Shooting "straight up and down" often gets to where you turn your elbow down instead of sideways like it should be. When you hunched over some you probably canted the bow more which gives more clearance similar to opening up the stance. I try to rotate my entire arm from the shoulder to the wrist. Thankfully, the wrist being the wonderfully versatile joint it is, you can pivot the bow from vertical to beyond horizontal without moving the elbow away from horizontal.
If that isn't the issue, the next most likely is too closed of a stance. If you are really upright and sideways to the target, especially if you hunch your bow arm shoulder forward AT ALL there is very little string clearance. Standing slightly more quartering towards the target will open up the angle between the line of the arrow and the line of your bow arm. So will just bending the bow arm slightly (if you keep the elbow sideways). Bending the bow arm is a bit tricky as too much and suddenly you feel like the bow is trying to come back at your face! Just slightly unlocked in the elbow is about right.
I'd try shooting with a couple things in mind. Open your stance just enough to get the clearance you need with your elbow rotated horizontal and keep your bow arm shoulder down. Your back tension may feel a little different but that doesn't mean it's not there. Changing the angle to the target changes the demand on your back muscles and may take some getting used to. If you feel wobbly, keep the stance that gives the clearance you need and concentrate mainly on pushing with your bow arm and following through on release.