Well I just changed one of the springs in my trunk that snapped. You can probably adjust it a bit and add more tension to the springs you have on the trunk. Mine is usually getting stuck to the rubber seal since we had it undercoated.
On each side there is a spring that has a bolt going through it, you can just tighten the bolt more, ( seeing les gap between the end of the spring and the mount that the bolt goes through).
That should give you more tension on the springs and might help open it more.