We got Sophie a month ago when she was 8 weeks old and of course she wasn't potty trained.She would pee and poop anywhere

Luckily we have tile floors all over the place so cleaning is piece of cake.I tried puppy training drops,but with no results.I used to put those drops on a paper in the litter box,but she would pee on the floor,away from the papers.But recently I got a playpen for children,big enough to put her doggy pillow,some chew toys,her food and water and a litter box.The first day she wouldn't go in the playpen.She messed the floors as soon as I got her out of it.But the next morning I was surprised to see that she DID go in the litter box.Still she won't poop in the litter box while she is in the playpen so I have to let her run around to do her business.I usually put papers on the floor,and she sometimes does her business on them,but there are a lot of accidents every day.Last weekend we were on a trip and we took her along.In the hotel I let her in my bed to play a little bit and she peed on the covers. It's not the first time when she does that.Sometimes we play and she suddenly stops and squats, right in front of my face.I wonder if she will ever get the idea where she is supposed to do her business.It's really frustating and I hate keeping her in the playpen too long.