Mixing up forms

Been wondering this for a while now...sometimes when I'm chatting away in Japanese using informal forms I'll forget how to say a word in the informal form and use the ~masu form. Of course if I had the time I could just quickly compute the mase form into the regular form, but conversation doesn't allow time for that. So I was wondering whether or not this would sound strange to a Japanese listener. Something like:

昨日京都に行った。とてもすばらしかった！古い道を散 歩したり舞子さんを見たりした。そして午後にラーメン屋で食べました。その店のラーメンはすごくうまかった！

So you can see there basically the only thing in the formal form is 食べました. Does it sound weird in there with everything else being less formal?

Tricky question. Basically Japanese _do_ mix up plain and polite forms but generally they switch between the two for a reason. If you switch at random then I dare say it sounds a little bit odd but I don't think it is a massive problem.

くだけて話しようとして、突然丁寧に返ってぎこちなると思いますが、大きな問題ではありませんよ。