I know this post is months old but just in case someone has this question in the future, I've seen this happen on other makes/models. There's a bit of a settling period that can sometimes happen when you install new struts. I doubt that you put them in upside down but that can cause the front to lift too. There's also always the chance that you got struts that weren't meant for your make/model but I doubt that too. I'd just give it time to settle and, if there's still an issue, maybe contact the manufacturer of the struts.