Yes, too weak. I think this is a raise or fold situation, you just happened to pick the wrong one. Your raise is for 3 reasons:

1)SB may not have an ace, he could have a draw and wants to push it.
2)If he does have an ace, your raise could scare him enough that he eases up on the turn/river and you may get to a showdown cheaply. So your raise will help a ton to find out how much he really likes his hand.
3)Whatever happens to be true, you definitely want the players AFTER you to fold like cheap tents so you can focus on the SB.

Plus, say the SB flopped two pair, you still have a good number of outs in order to draw out against him. So, this is a raise or fold situation, and raising is the better option.