If your work reference letter clearly states that you were employed full time, i.e., at least 30 hours per week for the duration that you have claimed, and your supervisor/HR manager backs up this claim -
if and when contacted by IRCC) - then you should be fine. It would be especially useful if you have included pay stubs and bank statements (showing deposits of your paychecks) for the duration of this employment. Also, remember that IRCC does not always authenticate every work reference letter with the employer, and the presence of other supporting documents - such as pay stubs, bank statements, income tax returns, etc. - is usually sufficient evidence for a case officer. For more information on what qualifies as full time v. part time work or what counts as skilled work under FSW, go here:
https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/express-entry/eligibility/federal-skilled-workers.html#skilled