Today is happywas a great Friday, and my schedule was full.

EMore specifically, the hardest task for me today was drafting.

Screws have many different kinds of product standards, so it was a painstaking task.

I got a stiff neck and run out of myI lost concentration.

I'm done today!

This sentence makes sense but it's not really consistent with the rest of the paragraph. Instead, you might say, "However, now I'm done" or "But now, I'm done for the day".

I'm so Ttired.

"Tired" should only be capital, if it is at the start of a sentence, not at the end. Only certain words remain their capitalization, such as names ("John", "Abraham") and place names, ("New York", "Kyoto") or weekdays ("Monday, Friday"). PS. Remember the periods at the end. Otherwise, great job!

Today is happywas a great Friday, and my schedule was full.

When talking about a day gone past in one sentence, use "was" instead of "is". "Is" implies a day to come or the current moment, and "was" implies a time gone by, something in the past.
Also, when referring that a day was happy or good, try to use "great".

EsSpecifically, the hardest task today was drafting.

This is a personal preference, but if I remember correctly in grammar, if you're talking about a specific event, you use "Specifically" instead of "Especially". Otherwise, great job!

Screws have many kinds of product standards, so it was a painstaking process.

When referring to a series of actions like you did above, I would use "a" to focus on that specific task, and after "painstaking" I would use "process" so the sentence becomes "a painstaking process" referring to the blueprint manufacturing mentioned above.

I got a stiff neck and ruan out of my concentration.

"Run" implies a current moment, and can't be used in a past tense. "Ran" implies that your concentration ran out. The "got" part was correct tho. Good job!