I've tried using all of them, healing teammates, laying down jammers, smoke ect. but my percent won't budge. Its the only one I don't have at 100%. I'm starting to think that theres some problem with the servers or something because I've been using every single gadget but I get no results.

What should I do? Any help would be greatly appreciated.

One of the most common problems is that you have to play ALL the maps to be able to get them up to 100%. Often a gamer will only play maps that they are most familiar with or best at, but to get the max you have to balance play across all of them.

so should I just play against bots on each map using different gadgets?

Yes, that or against other gamers.

The trick is that to get full credit for the gadget use, the gadget needs to actually affect the bot/player. For instance, the jammer needs to confuse the bot, the flash bang should blind them. You can use the med syringe when you get back to home base after getting injured or you can just carry them to heal, either seemed to work for me.

Have you done any of the co op challenges?

My gadgets were stuck on 84% for months then I did a few challenges and it changed to 100%