I have a tight feeling 3 days after my stretch mark and CO2 Fraxel laser treatment procedure, is this a concern? (Photos)

Redness and swelling are what usually happen for a few days after the procedure, and crusting starts day 2. The tightness could be just byproduct of the swelling- but if it's severe and/or doesn't begin to go away with the other symptoms during the next few days definitely check in with your dermatologist. 

You should expect a number of sensations. Skin getting tighter is expected. Feeling of tightness suggests to me you may not be keeping your skin moist enough. 
Over the next 7 days, keep your treated area VERY moist, then you can step down 50% - 70% in week 2 and 50% again in week 3. Keep in mind most your healing won't stop for 6 weeks or so, but some will continue for 5 - 6 months out. So continue with frequent moisturizing and keep treated area out of the sun. 
If you must go in the sun without good cover up on your arms, use high quality sun screen protection with high SPF value. Remember, you're generating new skin. Thin cloth won't provide adequate protection. You wouldn't put a new born baby in the sun. So don't do it to your arms.    
In general, your skin loves moisture, try to keep it moist all the time.  

For extensive CO2 laser - especially on the arms, legs and chest area, one should always be reviewed by your specialist at their chosen review date. This can make sure you are healing up OK, and any infection or skin colour changes identified, treated, or prevented. Each Specialist will have their own skin care routine post laser. From your pictures, it looks ok, but I don't know the laser settings, density, or power levels, so you do need advice from the Board Specialist who performed this. All the best, Dr Davin S. Lim. Brisbane, Australia.