Ako ay nasa Zoo 

Ako ay nasa Zoo. Nakakita ako ng elepante. Malaki ito. Nakakita ako ng Kabayo. Mabilis ito. Nakakita ako ng buwaya. Katakot-takot ito. Nakakita ako ng zebra. Guhitan ito. Nagkaroon na ako masaya

Salamat Po!

My first attempt ever to write sentences in Tagalog. Any advice is appreicated

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Hello! The highlighted parts were the ones I'm going to correct. 

Here, I'm assuming what you want to say is "It's scary". The term Nakakatakot ito  would be much better. Katakot-takot is often used to say "many". 

For the second part, I think what you meant is that you had fun. Nagkaroon na ako masaya is a very direct translation and would mean differently. Saying, Nasiyahan ako, Natuwa ako or Nag-enjoy ako would be better. 

I hope this helped. :)