I usually prepare 6-8 personal returns but one return will have a small business start up. Which programme should I purchase?

Because you are doing multiple returns, it is always best to choose the downloaded version: 

Home & Business can be accessed here: https://turbotax.intuit.ca/business-tax-software/home-business.jsp; this will enable you to do up to 20 returns as well as the small home business. 

My question remains... Can I file my small business (more like side gig) on my personal tax using standard Turbo Tax that I already purchased

Yes, of course you can and I recommended the Home & Business version to assist you.

Can i use the standard (i already purchased) instead of the home and business? Thats is my question:)