My timing belt broke i cant get it back in time, a

I recommend that first, you check your work to ensure that you have the cam and crank indexed properly. Next, do a compression test on the engine. If the compression is very low or not there at all in some cylinders, likely you have either bent some valves or punched holes in the tops of the pistons (or both). At that point, I'd still remove the heads to take a look. If pistons are "eyebrowed" from valve contact but do not have any major damage, you can sand off any pushed material from the damaged spots (otherwise it will cause detonation) Then depending on how much valve damage you have, either replace the heads or valves.If compression is similar in all cylinders but is generally lower than it should be, this is a good indication that the indexing is incorrect.
Could be it's blown, but don't give up till you have verified this for sure!!

If your timing belt broke while driving then I would agree with the mechanic, your motor has more than likely blown.Sorry to convey the bad news but I hope this helps.