Award Ceremony

Today, an award ceremony of an academic society was held in Tukuba, Ibaraki Prefecture, and I received a best-paper award.

Also, I performed a keynote speech after the ceremony in commemoration of the win.

Although I thought that this is a lonely expedition, I found that my former teacher was taking my picture when I was talking.

I was very surprised and a little unsettled, but I was really pleased.

In addition, he introduced me to many his friends, professors and officers at the banquet.

It was a fulfilling day.

I'd like to keep in touch with him in the future.

授賞式

今日は茨城県つくば市で学会の授賞式があり、私は論文賞を受賞しました。

そして、授賞式の後には受賞を記念して、基調講演を行いました。

今回は1人での寂しい遠征と講演だと思っていましたが、講演中に私の学生時代の恩師が写真を撮っているのに気が付きました。

かなり驚いて少し動揺しましたが、とても嬉しかったです。

さらに、その後のバンケットでは多くの教授方や運営の方に、私のことを紹介してくれました。

とても充実した一日でした。

今後とも仲良くさせて頂きたい思いです。

• Award Ceremony
• This sentence is perfect! No correction needed!

• Today, an award ceremony of an academic society was held in Tukuba, Ibaraki Prefecture, and I received a best-paper award.
• Today, an award ceremony of an academic society was held in Tukuba, Ibaraki Prefecture, and I received an award for the best paper.

• Also, I performed a keynote speech after the ceremony in commemoration of the win.
• Also, in commemoration for getting the award, I performed a keynote speech after the ceremony.

• Although I thought that this is a lonely expedition, I found that my former teacher was taking my picture when I was talking.
• Although I had thought that this is a lonely expedition, I realized that my former teacher was taking my picture while I was talking.

• I was very surprised and a little unsettled, but I was really pleased.
• This sentence is perfect! No correction needed!

• In addition, he introduced me to many his friends, professors and officers at the banquet.
• In addition, he introduced me to many of his friends, professors and officers at the banquet.

• It was a fulfilling day.
• This sentence is perfect! No correction needed!

• I'd like to keep in touch with him in the future.
• This sentence is perfect! No correction needed!

Yay congrats! It is certainly important to keep in touch with all these important people in our lives.^^

• Award Ceremony
• This sentence is perfect! No correction needed!

• Today, an award ceremony of an academic society was held in Tukuba, Ibaraki Prefecture, and I received a best-paper award.
• Today, an award ceremony of an academic society was held in Tukuba, Ibaraki Prefecture, and I received thea best-paper award.

  If there's only one, then "the" should be used instead of "a". However, if there are many best-paper awards, using "a" is correct.

• Also, I performed a keynote speech after the ceremony in commemoration of the win.
• Also, I performed a keynote speech after the ceremony in commemoration of the awardin.

  There was nothing wrong with the original "win", but using "award" is a little more humble. This is only style, not real correction.

• Although I thought that this is a lonely expedition, I found that my former teacher was taking my picture when I was talking.
• Although I thought that this wouldis be a lonely expedition, I found that (my/a) former teacher was taking my picture duriwheng myI waspeech talking.

  Because you thought it was lonely, but actually, it was different, I changed the wording to subjunctive "would be".
  
  I put a note that "a former teacher" could be appropriate as you probably have had many former teachers. "My former teacher" is not wrong, could be seen as dismissive of other former teachers.
  
  Also, I changed "when I was talking" to "during my speech". Again, original was not wrong, but this style sounds a bit more formal, which matches the rest of your post.

• I was very surprised and a little unsettled, but I was really pleased.
• I was very surprised and a little unsettled, but (in the end) I was really pleased (to meet him/that he came).

  Nothing grammatically wrong, but the original sentence sounds a little short. Possible additions are in ().

• In addition, he introduced me to many his friends, professors and officers at the banquet.
• In addition, he introduced me to many of his friends, professors and officers at the banquet.

  When using possessive pronoun like "his", you need to use "many of" instead of "many".

• It was a fulfilling day.
• This sentence is perfect! No correction needed!

• I'd like to keep in touch with him in the future.
• This sentence is perfect! No correction needed!

I think your English is already pretty much perfect!