It was designed and made by myself and take me 2 hours to complete this建议应改成It was designed and made by me and I spent 2 hours doing this.因为原句中,take的主语虽然是it,但与was前的it指代不同.最好用spend改写,避免产生歧义.
You should know what a challenge this is for a young man!建议删去should.