My coolant level was low and I added some different coolant to the tank

I HAVE A 2000 FOR EXPEDITION XLT. The car has been running fine and having no problems. My friend indicated that my coolant level was low and put some coolant into the reservoir tank. Now since he did that, I smell coolant as well as my temperature okay, my car has been run ning perfectly fine. Few days ago, friend of mine noted that my fluid levels were low for coolant and added some coolant to the tank. It was the right kind but I dont think it was 50/50 mix. My car has not been running hot or anything before this date. Now, the temperature gauge is going up to almost hot and goes back down and I can smell coolant. Someone else told me that it is because of the fact that there was no water put in at that time. Any suggestions because I dont want it to run hot and create a problem that I didnt have! Thanks