I’ve just recently found out that when we’re washing our arms from the elbow, we’re supposed to wipe all the way down to the finger tips. I’ve only been washing from the elbow to the wrist. My hands were still wet with wudu water however due to using them to wipe my arms. Does this mean my wudu has been invalid for all this time and do I have to make up all my salah again?

Yes you need to make up the wudhu and the prayers.