No. Run away from a saddle that bridges for a 3 year old. Often as the horse gets older the withers and shoulders developing will make it worse as the horse is worked. It's a really good way to get bucked off.
The panels should make even contact throughout. No bridging anywhere... bridging is a sign of BAD fit. You should be able to slip a flat hand under the saddle, and slide it down the front (under the points of the tree) without any gaping to tight spots. You should be able to do the same from front to back, no bridging, no tight spots.
If it is bridging in the middle, that means it is most likely tight on the shoulders/ wither and at the back of the panels towards the cantel, making a 'bridge'. Ouch!
As the horse fills out, you can expect the front of the saddle to get tighter, causing even more bridging.
I too have a young horse, luckily for me ($$ wise) a wintec adjustable saddle is fitting well (no bridging any where, no dry spots, lots of panel contact, tons of wither / spine clearance). I have had to switch plates (from M to MW and back) a few times as she has developed, added and dropped weight etc.
Now that she is 4 1/2 and settling into a size, I am hunting for a new, permanent saddle.